[2.2.x./2.3.x, Accessibility] Apply accessibility guidelines in the features that have been developed in the latest releases by the MAAS team and are not accessible

[Maria Vrachni]

[2.2.x./2.3.x, Accessibility] Apply accessibility guidelines in the features that have been developed in the latest releases by the MAAS team and are not accessible

A number of features have been implemented in the last two releases that do not comply with the accessibility guidelines (Aria labels, tabbing through the UI etc)

Bug description:

* Current result:

Given I am the MAAS web application following the 2.1 release
When I am trying to access the new features with my keyboard or a screen reader
Then I probably can't

* Expected/ correct result:

Given I am the MAAS web application following the 2.1 release
When I am trying to access the new features with my keyboard or a screen reader
Then I should be able to

[OS X Sierra]

Chrome, Version 61.0.3163.79 (Official Build) (64-bit)

Screen size: 15.4-inch (2880 x 1800)