Corebird 1.2 release.

• Inline media and avatars are no longer cached on disk
• Videos now indicate download progress showing a preview thumbnail with a circular progress overlay
• We download higher-resolution avatars on HiDPI displays now
• The build system usage has seen a major refactoring an cleanup, thanks to Rico Tzschichholz
• The sidebar is now at the top and dark
• Favorites now us a heart icon
• Sending tweets is now cancellable (e.g. when multiple images are attached, in which case it might take a while)
• Inline media are now displayed "full-size", scaled to the current window size.
• Instagram videos are now correctly marked as videos, instead of was images
• If you have GTK+ >= 3.19, there's now a GtkShortcutsWindow accessible from the app menuexplaining the various keyboard shortcuts. Note that Corebird still compiles and runs with GTK+ 3.16
• The big "add media" button in the compose window has been replaced with a regular text button. The added images are scaled down and displayed below it
• You can quote your own tweets now
• The settings dialog now contains a setting to hide "inappropriate content", and it is enabled by default.
• The file selection dialog in the compose window now keeps you from selecting files > 3MB.