Docs: Update "Holds Management" section for web client

[Remington Steed]

We need to update the "Holds Management" section for the web client.

http://docs.evergreen-ils.org/dev/_holds_management.html

It should only required the following changes, but review of the whole section is also welcome.

TODO: Remove reference to "Print Full Pull List (Alternate Strategy)".
- http://docs.evergreen-ils.org/dev/_managing_holds.html

TODO: Replace screenshot holds-managing-16.png
- http://docs.evergreen-ils.org/dev/media/holds-managing-16.png
- On this page: http://docs.evergreen-ils.org/dev/_managing_holds.html

[Gina Monti (gmonti90)]

submitted some fixes on this

[Jane Sandberg (sandbergja)]

Thanks, Gina! I pushed your fixes to master, rel_3_8, and rel_3_7.