Apply syntax highlighting to fenced code blocks client-side

Instead of applying the syntax highlighting scheme class to these blocks
server-side, we use Javascript and Gon to apply the user's color scheme
(or the default) client-side.

This will make it easier to cache these blocks in the future because
they're no longer state-dependent.

See merge request !1203

Update PreferencesHelper specs

Signed-off-by: Dmitriy Zaporozhets <dmitriy.zaporozhets@gmail.com>

Instead of rendering this value server-side, we use Javascript and Gon
to apply the user's color scheme (or the default) to any syntax
highlighted code blocks.

This will make it easier to cache these blocks in the future because
they're no longer state-dependent.

Very similar to Gitlab::Theme, this contains all of the definitions for
our syntax highlighting schemes.

Reply by email

Fixes #1360.

It's far from done, but _it works_.

See merge request !1173

Fix bug preventing invite by e-mail

This was broken in 70f5291808 as a result of introducing the ability to filter by current user.

Closes #2320

See merge request !1181

This was broken in 70f5291808 as a result of introducing the ability to filter by current user.

Closes #2320