Resolve cross-domain error causing infinite-scroll to fail on HTTPS

Safari on Desktop and iOS consider HTTPS to HTTP requests as cross-domain.
So, for example, if a site is accessed via HTTPS on iOS Safari, infinite scroll will fail.

This bug affects many more users on wordpress.com, where all logged-in users
are switched to HTTPS.

The issue is resolved by checking the current protocol in infinity.js,
then switching http:// out for https:// in ajaxurl if needed.

This method is preferred over changing ajaxurl on the PHP side, beceause
server-side caching may cause protocol detection to be unreliable.

Video of bug in action:

https://www.youtube.com/watch?v=253litAe1sg
Portfolios: use correct columns variable

Fixes a typo where the wrong variable was provided in the `portfolio-project-post-class` filter hook.
REST API: Improve endpoint paths.

POST /sites/%s/plugins/%p { active: false } (deactivates module p on
site s)
POST /sites/%s/modules/%m { active: true } (activates module m on site
s)
REST API: Tidying spaces.
REST API: Use safehtml for module's description
REST API: Add get module endpoint.
REST API: Define common properties in the parent.
REST API: Improve error identification.
REST API: Not found plugin should return 404.
REST API: Ooops, wrong parent class.
REST API: Add request format.
Merge pull request #899 from Automattic/proper-endpoints-paths

Proper endpoints paths
Settings: Keyboard Accessibility.

Make the activate/deactivate/configure links keyboard accessible.

The compiled CSS is coming in a subsequent commit.
Commit compiled css from previous change set.

Changed in e64ec4889455818fd7f76096d13d88b05581ac6e
Add a title/description extractor and compiler.

For v3.2 and on, this will let us translate module headings without a
custom parser, and will work more gracefully with the WordPress.org
plugin translation glotpress install.

Please don’t commit the results to the repo yet, as we don’t want new
strings in our current wpcom glotpress for 3.1 this close to release.
Carousel: Remove README. Sorry Team Downing Street.
Never inc modules that need connection in dev mode

Fixes #905
Settings: Don't trigger search event on tab.

Keeps checkboxes checked when going back and forth with keys only.
Merge pull request #907 from Automattic/ticket/903

Better keyboard accessibility for modules listing page
Related Posts: set `font-size` for links

Set `font-size` for related post links to ensure consistent display
across themes.

Closes #485