Release 3.27.1, 2017-12-09
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* User-visible improvements:
 - Draw non-breaking spaces.
 - File browser in the side panel: popup menus under buttons.

* Port to GtkSourceView 4 and Tepl 4.

* Internal code refactorings, use more Tepl features:
 - Use more Tepl GActions.
 - Let Tepl handle the window title.
 - Implement TeplAbstractFactoryVala subclass.
 - Other small things.

* Port to GAction/Amtk:
 - Port the whole LaTeX menu to GAction and C in the liblatexila.
 - Math menu in progress.
 - Create first AmtkActionInfo.

* Other small improvements.
* Translation updates.