Added MySQL database configuration to the docs

Documents changes made in #1370 that resolves #1332

Database Admin React conversion + UX improvements

Fix tooltips on dashboards

Improved loading page

Allow Metabase to use MySQL for the application db

Fix metadata section popovers not closing, and save indicator not updating

it would be good if i could spell properly.

update our deployment command in circle.

support RDS environment variables in our bin/start script

add a couple of MySQL specific mods to our migrations where we need to use the `TEXT` type instead of `VARCHAR` on mysql.

Mostly working conversion of database edit/create to React. Also incorporate some of the UX improvements (delete confirm, animating FormMessage)

Dockerfile 

Bump dependencies.

fix em dash

highlight file path as code

more consistent highlighting

State that only H2 and Postgres are available

add exceptions for epl libraries