Merge tag '0.4.0' into develop

0.4.0

* tag '0.4.0':
  Add icon and move screenshots
  Update docs
  Bump version number
  Major refactoring
  Fix the insert Gistpen popup
  Fix insert Gistpen dialog
  Type checking
  Fix failing tests for content
  Enqueue css only on edit screen
  Fix inhertiance in TinyMCE pop-up
  Filename smaller h2->3
  Need to remove filters in the updater
  Fix bug that would delete languages without reinstalling