InlineMediaDownloader: Use media instanste in get_xx_path
Fix examples/mm_widget.vala
tweet-list-entry: Add MultiMediaWidget
test/multimedia: Enable again

Now that InlineMediaDownloader works correctly, we can use this.
TweetListEntry: Use MultiMediaWidget

etc etc etc
tests/inlinemediadownloader: Add too_big test

Tests what happens if the user sets the maximum size for inline media to
something low and then tries to download a media that is just bigger
than that limit.
MultiMediaWidget: React on media load
InlineMediaDownloader: Remove the 2 suffix

This was only used temporarily when the old implementations still
existed and is not useful anymore.
MultiMediaWidget: Redraw on media load
Utils: Try to use a thumb height + width...

... instead of just one size. Thumbnails will probably not be squared
anymore in the future.
InlineMediaDownloader: Use dymanic thumbnail sizes