Use white for base font color, teal for headers

This prevents having to override for white all over the place.
Show "Loading..." and "No running tasks" in App modal

"Loading..." is the initial state, and "No running tasks" displays after
the collection has been synced.

Fixes #95.
Merge pull request #96 from mesosphere/empty-task-list-message

Empty task list message
Show error message in task table if fetch returns error

Previously the task table would show "Loading..." permanently if the
server returned an error.
Re-compile JS for task list errors
Make tests pass on all locales