Reduce the number of document jquery objects created

[mattfarina]

The horizon codebase regularly creates jQuery objects based on the document (`$(document)`). This can happen many times in the same scope. For example, https://github.com/openstack/horizon/blob/1385db8d1f8358aca190a40ed4c341bfc3e46f56/horizon/static/horizon/js/horizon.instances.js shows it happening 8 different times.

This could be done once, saved to a variable, and then reused. Creating a jQuery object isn't cheap. By doing it many times as opposed to 1 we are causing more logic to fire, more memory to be allocated, and more work to happen in the browsers garbage collection.

By moving to a single variable and repeatedly using it we will use less memory, cause horizon to be faster, and other performance benefits.

[OpenStack Infra (hudson-openstack)]

Fix proposed to branch: master
Review: https://review.openstack.org/148957

[OpenStack Infra (hudson-openstack)]

Reviewed: https://review.openstack.org/148957
Committed: https://git.openstack.org/cgit/openstack/horizon/commit/?id=b48789e65704adf92737baccf245cc611b013e05
Submitter: Jenkins
Branch: master

commit b48789e65704adf92737baccf245cc611b013e05
Author: Matt Farina <email address hidden>
Date: Wed Jan 21 09:45:20 2015 -0500

    Remove extra jQuery object creation in horizon.instances.js

    Reduces the number of jQuery document objects from 8 to 1 using a variable.
    Removes the creation of redundant jQuery objects based on a selector.

    Change-Id: I9ed0815f4fd171cec49c66b73cc04addd46c820d
    Partial-Bug: #1412971

[OpenStack Infra (hudson-openstack)]

Fix proposed to branch: master
Review: https://review.openstack.org/151275

[OpenStack Infra (hudson-openstack)]

Reviewed: https://review.openstack.org/151275
Committed: https://git.openstack.org/cgit/openstack/horizon/commit/?id=52f401457f4cbf37e52c92c7c27ac42710b54098
Submitter: Jenkins
Branch: master

commit 52f401457f4cbf37e52c92c7c27ac42710b54098
Author: Matt Farina <email address hidden>
Date: Thu Jan 29 10:15:28 2015 -0500

    Updates contribution guidelines for JS object performance

    In a new section, titled performance, a requirement is added
    for JavaScript code to limit the re-creation of objects in
    the same scope. An example with jQuery is given with explanation.

    Change-Id: I2f0d8392277f65384389d8d20154d645197050af
    Partial-Bug: #1412971

[OpenStack Infra (hudson-openstack)]

Fix proposed to branch: master
Review: https://review.openstack.org/152908

[OpenStack Infra (hudson-openstack)]

Reviewed: https://review.openstack.org/152908
Committed: https://git.openstack.org/cgit/openstack/horizon/commit/?id=fe2dc1d8acc11e3e9a16264aed6bb62c21769582
Submitter: Jenkins
Branch: master

commit fe2dc1d8acc11e3e9a16264aed6bb62c21769582
Author: Matt Farina <email address hidden>
Date: Wed Feb 4 06:24:50 2015 -0800

    Remove extra jQuery object creation in horizon.modals.js

    Reduces the number of jQuery document objects from 7 to 1 using a variable.

    Change-Id: I7b1bf71512c1913854f94767b475fc04ecad2afc
    Partial-Bug: #1412971

[OpenStack Infra (hudson-openstack)]

Fix proposed to branch: master
Review: https://review.openstack.org/162650

[OpenStack Infra (hudson-openstack)]

Reviewed: https://review.openstack.org/162650
Committed: https://git.openstack.org/cgit/openstack/horizon/commit/?id=2a8cad06742130eda7148ca6534c30cdf36c1dec
Submitter: Jenkins
Branch: master

commit 2a8cad06742130eda7148ca6534c30cdf36c1dec
Author: Chris Johnson <email address hidden>
Date: Mon Mar 9 10:59:34 2015 -0400

    Refactor multiple references to $(document)

    According to the Horizon Contributing Guide, we are to:
    "Avoid creating instances of the same object repeatedly
    within the same scope. Instead, assign the object to a
    variable and re-use the existing object."

    The guide references the use of "$(document)", as an
    example. And yet multiple examples can be found of that
    sort of approach. This commit cleans up those references.

    Partial-Bug: 1412971
    Change-Id: Ica05700101ae9a453623d928f07b75fa7aaca186