Override registerClientScript() since we don't need any scripts
(fixes #20)
added Controller::registerScripts() which registers Bootstrap and the
image lazy loader
use tabs instead of spaces
cache font files (fixes #21)
removed some unused variables (fixes #19 and #13)
use findByPk() instead of findByAttributes(), fixes #16
updated Thumbnail class description (fixes #18)
properly validate settings (fixes #17)
allow normal users to change backends (broke in
340eacfb81cbe4482475b4cca7d12768748b2855)
cache the main menu when only a single backend is configured
added a base class for simple migrations that only add a setting
added option for caching all API calls (can be useful on slow hardware
like the Pi)