Updated Brazilian Portuguese translation
Make the timeline insensitive during rendering by hijacking all events

Fixes bug #709468
mainwindow: Compact the ProjectManager signal connection code
Use icon_name all over the place, as stock icons are deprecated in GTK+ 3.10
Updated Czech translation
Updated Spanish translation
Updated Brazilian Portuguese Translation
help: Update the logo image for the user manual

Also use a smaller version of the icon to be consistent with other applications
help: Also mention Pitivi's license on the user manual's license page
help: Add a tip on how to remove middle portions of clips in splitting.page
help: Update importing.page, movearoundtimeline.page and usingclips.page
help: Create a new page in the user manual to explain grouping
help: Add the "keyseq" tag where appropriate

- Use it instead of <key>key</key>+<key>key</key> in movearoundtimeline.page
- Use it instead of <key>key+key</key> in cheatsheet.page
help: Document better the procedure of creating new layers

Fixes bug #720878
elements: Fix RoundedRectangle.get_border_color parameters
timeline: Always set self.current_group in TimelineStage._dragEndCb
timeline: Selection cleanup
timeline: Remove Selection.last_single_obj as it's not used
project: Avoid setting the selection field for a GESTimeline object

We set and use TimelineStage().selection = Selection().
The GESTimeline().selection = Selection() field removed in this commit
was simply not used anywhere.
timeline: Remove unused addClip method