previewers: stop waveforms and thumbnails generation when removing clips
elements: Set clip inpoints to prevent keyframes from breaking on split/trim

Fixes bug #709784
build: Don't attempt locale-uninstalled bits if DESTDIR is set

This breaks the build in Continuous, because it has a read-only bind
mount outside of the explicitly provided $DESTDIR, and we were
attempting to write files outside of that area.

https://bugzilla.gnome.org/show_bug.cgi?id=710833
Drop dependency on PyXDG, use GLib instead

There's really no reason to depend on an external Python library when
GLib has a perfectly good implementation already exposed via
pygobject.

Specifically I don't want to pull in pyxdg to gnome-continuous.

https://bugzilla.gnome.org/show_bug.cgi?id=711184
Drop use of old "glib" module

It's not shipped in gnome-continuous, and we were just using
it for markup_escape_text which works fine via gi.repository.GLib.

https://bugzilla.gnome.org/show_bug.cgi?id=711184
Fix XDG user dirs regressions from commits 8159d2374 and da87a41ce

Add the missing import for GLib, and fix the subtle change in subdirectories:
~/.cache/pitivi/pitivi/ was used instead of ~/.cache/pitivi/
and ~/.config/ was used instead of ~/.config/pitivi/
previewers: Kill copy-pasted code
Apply minor changes to make AppData XML file friendlier to distributions

Some distros absolutely require a copyright header on this file.
Also, the license XML tag is not for the app, but for the xml file itself.
Finally, the image width and height parameters are entirely optional.
Keep the welcome dialog shown when clicking "Missing dependencies..."

Also prevent GTK3 from messing up the size of the missing dependencies dialog,
and remove an unused import in timeline/timeline.py

Fixes bug #711357
ui/startupwizard: Force ButtonBox items to have a homogeneous/uniform width

Fixes bug #682766
Releasing Pitivi 0.92 "Baby Steps"
Uploaded Ukranian
Make pitivi.appdata.xml more translation-friendly and pass appdata-validate

- Make individual description items translatable instead of _description
- Move the summary contents into the description to avoid length issues
- Remove "name" and "summary", rely on pitivi.desktop instead
Updated Brazilian Portuguese translation and proofread
Updated Polish translation
Uploaded Ukranian
Updated Spanish translation
Render: don't use the caps name for the muxer / encoder caps.

Instead use their stringified version.
Makes us able to render in MP4 and MPEG-TS.
bin: git-environment: Fix mixup in variable names
Updated Traditional Chinese translation(Hong Kong and Taiwan)