Disable pointer events for disabled buttons
Missing semicolon
Added information about missing scripts
Added generic alert messages implementation

Generic messages can be created by calling `PTL.msg.show()`, passing an
object of key-value pairs as a parameter. The object accepts the following
keys:

  - 'text': the message to be shown.
  - 'level': the level of the message; can be 'info', 'warning' or
             'error'. By default, 'info' is used.
  - 'language': the code of the message's language.
Use the generic messages
Moved editor filtering and navigation to the action bar

The changes include:

  - The bottom toolbar is now gone.
  - The filtering controls are now part of the breadcrumbs, and will be
    merged with the search box eventually in the future.
  - The navigation controls are now at the top of the editor.
  - The export view link is now provided as part of the first drop-down.

Fixes #84.