Update redirects in specs, fix Build#new

Redirects for some UI actions were made more user friendly in the
last commit, and the specs are now updated to match. Build#new
had an issue when visiting builds_path (instead of
project_builds_path). Both situations are now function as expected,
and all specs pass.
Build updater script only runs on Build#show

Adds a check before kicking off interval update script that window
path looks like /builds\/\d+.
Add JavaScript update of SHA during build process

Adds a span.js-build-sha within the SHA <dd> tag on Build#show. The
javascript updater checks if it has been set and updates from
build.sha. The `sha` attribute is now served from the build#show
jsbuilder.