Migrate to Mergely 3.3.4.

RhodeCode 2.2.5 distributed Mergely 3.3.4 with some of the changes that
Mergely 3.3.3 in RhodeCode 1.7.2 also had. That do however not seem to be
changes we want for Kallithea this way and we take the 3.3.4 files as they are.

I've also included the Mergely license file, as downloaded from:
http://www.mergely.com/license.php

That LICENSE file is kept in HTML just as it was downloaded from their
website. While it's a bit annoying to keep the license file in HTML, this is
the way it came from upstream so we'll leave it that way.

Since the Javascript code is used with other GPLv3 Javascript, we are using the
GPL option of Mergely's tri-license.

Finally, note that previously, this was incorrectly called "mergerly", so the
opportunity is taken here to correct the name. That required changes to
diff_2way.html.

As commands::

$ wget -N --output-document LICENSE-MERGELY.html http://www.mergely.com/license.php
$ hg add LICENSE-MERGELY.html
$ hg mv rhodecode/public/css/mergerly.css rhodecode/public/css/mergely.css
$ hg mv rhodecode/public/js/mergerly.js rhodecode/public/js/mergely.js
$ sed -i 's,mergerly\.,mergely,g' rhodecode/templates/files/diff_2way.html
$ ( cd /tmp; \
wget -N http://www.mergely.com/releases/mergely-3.3.4.zip; \
unzip mergely-3.3.4.zip )
$ sha256sum /tmp/mergely-3.3.4.zip
87415d30494bbe829c248881aa7cdc0303f7e70b458a5f687615564d4498cc82 mergely-3.3.4.zip
$ cp /tmp/mergely-3.3.4/lib/mergely.js rhodecode/public/js/mergely.js
$ cp /tmp/mergely-3.3.4/lib/mergely.css rhodecode/public/css/mergely.css
$ sed -i -e '/^ \* Version/a\ *\n * NOTE by bkuhn@sfconservancy.org for Kallithea:\n * Mergely license appears at http://www.mergely.com/license.php and in LICENSE-MERGELY.html' rhodecode/public/js/mergely.js rhodecode/public/css/mergely.css

Imported some of the GPLv3'd changes from RhodeCode v2.2.5.

This imports changes between changesets 21af6c4eab3d and 6177597791c2 in
RhodeCode's original repository, including only changes to Python files and HTML.

RhodeCode clearly licensed its changes to these files under GPLv3
in their /LICENSE file, which states the following:
The Python code and integrated HTML are licensed under the GPLv3 license.

(See:
https://code.rhodecode.com/rhodecode/files/v2.2.5/LICENSE
or
http://web.archive.org/web/20140512193334/https://code.rhodecode.com/rhodecode/files/f3b123159901f15426d18e3dc395e8369f70ebe0/LICENSE
for an online copy of that LICENSE file)

Conservancy reviewed these changes and confirmed that they can be licensed as
a whole to the Kallithea project under GPLv3-only.

While some of the contents committed herein are clearly licensed
GPLv3-or-later, on the whole we must assume the are GPLv3-only, since the
statement above from RhodeCode indicates that they intend GPLv3-only as their
license, per GPLv3§14 and other relevant sections of GPLv3.