l10n: Update Japanese translation
Updated Czech translation
dogtail tests: Fix the media library test to be able to "Select unused clips"

This requires GTK+ 3.8 or newer to work, as GTK entry widgets' clickable icons
were not accessible to AT-SPI in earlier versions (bug #686347).
Updated Slovenian translation
This commit adds a waveform audio previewer.

	+ previewers: Adds an audio previewer.
	+ elements: Add this previewer as a child of audio elements.
	+ Adds a new folder "coptimizations"
	+ Adds a new C extension, renderer, which renders the
	  samples on a cairo surface.
	+ Makefile.am:
	+ /* Fallthrough */
	+ configure.ac:
	+ autogen.sh:
	+ Updates to compile the renderer.