Add New Feature Flags Admin UI

[tn3rb]

For the E2E tests that @alexkuc is developing, we needed to remove the feature flags filter that was in the "Barista for Event Espresso" add-on, that essentially turned ALL of the flags on (for development purposes), because he needs manual control over them which he will do via WP-CLI.

This of course meant that there was no longer a way to turn those filters on for anyone that doesn't use WP-CLI.

This PR:

• adds a new tab to the EE Maintenance admin page named "Feature Flags"
• adds a series of switches for enabling or disabling individual feature flags
• refactors some of the logic in the EDTR (specifically the bulk edit feature) so that things can be modified directly via the new feature flags admin.
• removed the show/hide button for the bulk edit functionality
• the bulk edit UI will now always show when using the Entity List table view in the EDTR
• fixes some other style issues I noticed

Here's what the new admin page looks like:

And here's what the Event Dates List and filters look like in table view after the changes:

testing notes

• log into the admin and go to the WP Plugins admin page
• activate the "Barista for Event Espresso" plugin
• go to EE Maintenance admin page and click on the "Features Flag" tab
• toggle ALL switches off and click update
• [x] confirm that changes update correctly
• try toggling one or more feature flag switches ON and click update
• [x] confirm that changes update correctly
• [x] confirm that navigating away and returning to page still shows same settings
• turn ALL feature flags off again and click update
• in another browser tab, go the the Events admin page and add/edit an event
• toggle one of the feature flags to ON and click update
• refresh the event editor and look for the new feature / functionality
• [ ] confirm that toggling the feature flag switch affects the UI accordingly
• continue toggling each feature flag switch in the new UI and checking that the corresponding feature/functionality has changed in the EDTR
• [ ] confirm that everything works as expected

[alexkuc]

force-push due to rebase with master branch

[alexkuc]

/run-e2e

[garthkoyle]

I tested all the feature flags and they all work except the Bulk Editor:

[garthkoyle]

Scratch that, after switching from master to this branch I forgot to run yarn run build.

After yarn run build it is working.

[alexkuc]

/run-e2e

[alexkuc]

Restored & deleted branch to re-run E2E tests