timeline: Move text constants in the method where they are used
timeline: Disable the selection actions when timeline focused but there is no selection
timeline: Avoid calling a callback method directly
timeline: Get rid of method used in a single place
timeline: Test directly the element, not its parent
timeline: Be more strict when a timeline element is added
timeline: Set the mouse field in the constructor
application: Remove unused signals and methods
Move the gitignores to a single file
bin: Make sure we use python2 when python3 is the default
Remove retired maintainer from the DOAP file aimed at packagers
Remove obsolete svn file
pipeline: Raise an exception when setting the timeline fails
pipeline: Simplify logging of obtained duration value
project: Add the aspect_ratio dynamic property
tests: Allow the tests to be run by frameworks like nosetests
mainwindow: Reuse in_devel from configure
mainwindow: Make the version display more robust in the about window

Also add a unittest for the latest version logic and
moved the Pitivi tests to test_application.py because
that's the module where the Pitivi class resides.
mainwindow: Remove unused variable setting logic
mainwindow: Close the previewer only when the user pressed ESC or Q

The main problem was that if the user tries to click the playback bar to
play at a different position, it happens too often to get the mouse
cursor outside of the window and then the dialog was closing.

- Also allow using SPACE to toggle playback.
- Also moved the preview UI logic to a new PreviewAssetWindow class.