Homepage fixes

[benlk]

Changes

This pull request makes the following changes:

• Changes how constants are defined to reduce the amount of PHP notices that get dumped to the log
• Fixes the header image being wider than its container at specific viewport widths
• Fixes the black image overlay appearing underneath following elements on the page, by adjusting the z-index of an ancestor element
• Cachebusts one of the stylesheets
• Replaces fake search button in mobile nav at certain viewport widths with an actual search button

Why

For #7

Testing/Questions

Features that this PR affects:

• homepage , particularly the search in the nav

Questions that need to be answered before merging:

• [x] Is this PR targeting the correct branch in this repository?
• [x] Does the search work in other screen sizes?
• [x] Should we cachebust other stylesheets
• [x] Are we worried about the ridiculous number of stylesheets on this site and do we want to investigate a plugin that might concatenate and/or tree-shake them?

Steps to test this PR:

1. Check it out, then view it at many screen sizes
2. Play with the search in the menu
3. Play with the hoverable elements on the page

[joshdarby]

Are we worried about the ridiculous number of stylesheets on this site and do we want to investigate a plugin that might concatenate and/or tree-shake them?

We can probably worry about this in #3

Fixes the header image being wider than its container at specific viewport widths

This looks good

Fixes the black image overlay appearing underneath following elements on the page, by adjusting the z-index of an ancestor element

This looks good

Replaces fake search button in mobile nav at certain viewport widths with an actual search button

This looks good, but I'm seeing an unstyled search button from 970px to 768px?

This branch:

Master:

[benlk]

Should be fixed now.