Add fragment caching around expensive queries

* build_time_history
* recent project performance stats
Fragment caching in most tables, and elapsed time calculated client-side
Added action caching
Clearer jQuery usage and other feedback responses
Switch get param from tag to modified
Add explicit settings for config.cache_store
Go back to --force for git push in update_branch

If the promotion ref is manually updated by a developer they expect
Kochiku to overwrite it.
Switch from git cherry to git merge-base --is-ancestor

merge-base is the appropriate command to use in a programmatic situation.
Checks for @current_build before js
Merge pull request #87 from square/rob/update-like-you-mean-it

Use `git push --force` during promotion
Merge pull request #77 from square/rob/lil-caching

Introduce fragment caching
Now using median time for project show