Bump webkitgtk3 max version to 2.0.x

We build and run fine with this version of WebKitGTK, and have for
some time on Fedora 19, so no reason not to support this release.
Closes #5947 More padding in conversation list
Add copyright to geary.appdata.xml
Fix autocomplete matching; fix #7543

I had broken it fixing some unicode issues with autocomplete recently.
Handle null subject properly; fix #7326
Mail w/ only inline image not display: Closes #7563

Problem with internal processing of message not recognizing that
the ImageReplacer's HTML qualifies as "processed" HTML.
Added summary to appdata file
Closes #6611 Help updated for 0.4
Build with WebKitGTK 2.2.0: Closes #7023

Unfortunately, CMake doesn't allow us to exclude WebKitGTK 2.1.1
to 2.1.90.0, which are the versions that don't have the symbols
we need to build cleanly.  We'll have to assume that anyone building
with an installed WebKitGTK package is using a stable release.
Index attachment filenames properly; fix #7575
Check for null email store before using; fix #7566
Closes #7508 Composer edit box is now in a GtkFrame
Closes #7374 Fix various holes were drafts weren't deleted
Check for null text part; fix #7584
Closes #7560 Fix for wacky unread counts on first run
Revert change in ec032d5b: Refs #7023

Mistaken support for webkitgtk3 2.2.0, will have to wait for later.
Closes #7456 New icons from Sam Hewitt
Update translations from Transifex
News/Changelog for 0.4.0
Fix git archive to not include debian directory

Not sure if something changed in git, but we discovered the debian
directory was being included in the dist tarball, after Geary 0.3.  This
change seems to fix it in modern git.