Deploy Angular.js to static login page

Changes:

 - Change login button type to "button" (from "submit")

 - Disable button when no credentials are typed.

 - Display an error box (after textareas) when login credentials are
   erroneous. For now, hardcoded credentials (user:foo, pass:bar)

TODO:

 - (Maybe) Rewrite the login controller (as a directive for
   credentials). This would potentially solve some issues (error box not
   shown each time etc.)

 - Cosmetic changes to button (e.g. adding Bootstrap's
   "data-loading-text" when clicked)
Merge branch 'tracer-devel' of https://github.com/modernist/Alitheia-Core into tracer-devel