Improve accessibility of the home page

[jmclaus]

This is first pass at improving the accessibility of the home page:

• Use anchors instead of spans for actions that lead to a different page.
• Use buttons instead of spans for actions that open a popup.
• Avoid buttons in anchors.
• Adapt related CSS in homepage.gss to reflect the above and remove unused classes.
• Set an outline that is identical to the one reinstated in the instructor application.

All the clickable GUI elements are now accessible via TAB or SHIFT+TAB and will display an outline when receiving focus. That excluded the bottom left Experimental Design list that should be coded with list items containing anchors instead of divs.

This is rather simple to test, tab through every element and check that the action is correct when ENTER is pressed for a link and ENTER or SPACE is pressed for a button.

[jmclaus]

@annagav The failed test is weird, it happens on collecstatic. I may be because of the Travis update that happened 2 days ago. I'll investigate.

[jmclaus]

@annagav @pdpinch The build failure seems to come from the Travis update; by curiosity, I retriggered a build on latest commit on develop, it failed, again on ./manage.py collectstatic --noinput. It passed 10 days ago. Can someone from devops look into this? Thank you.

[pdpinch]

@starteam/devops can you look at the Travis failures?

[pdpinch]

@jmclaus do the tests pass locally?

[jmclaus]

@pdpinch Yes and if I add here the changes that @blarghmatey did to .travis.yml in his PR they also pass :) I'll remove that commit and rebase once it has has been merged.

[jmclaus]

@pdpinch @annagav I got rid of that last commit and rebased. Tests are all passing.