Docs: Small cleanups
Docs: Moved changelog for 2.5.2 to the release notes

First step in the plan to remove the changelog.
Remove git commands from Makefile

This allows the Makefile to work for the tarball.  Make sure release
guide include git submodule update actions.
New methods for getting stats

This incorporates commits (with necessary changes for our code base):
https://github.com/evernote/pootle/commit/f7bfd01d66b6c7e846be756a39318369d0884415
https://github.com/evernote/pootle/commit/7c89432a5a79db98176e7faf5e487a2164d650ff
https://github.com/evernote/pootle/commit/2d175ba08d4e82b0277708791cdff9ca21620d27
https://github.com/evernote/pootle/commit/76130849e2111c4c415e1d33cd274f53256124a8
https://github.com/evernote/pootle/commit/2de66822ed4a949b9bb3d9d9dab6c7988d2f40ea
https://github.com/evernote/pootle/commit/3591186540d2f049f5653910e78b0987dee9b9ef
https://github.com/evernote/pootle/commit/9e9031d8aec1309698491725e2d9dc7328eb8975
FOLLOWUP: Adapt our code
lastaction member stub
Implement get_name method override for the Directory object
Hide placeholders and table headings until the table is loaded

To indicate the table is loaded, remove 'js-not-loaded' class name from the stats table
Added JS for stats loading
Add progressbar js-based rendering
Add last-activity snippet
Use mtime as timestamp instead of isoformat to get a last action
Set default empty value for get_last_action method, add get_parent function
Delete getquickstats
FOLLOWUP: Adapt our code
FOLLOWUP: More code adaptation

As a side effect we no longer try to generate stats immediately after
updating against templates or from VCS, as I think this should speed
those operations considerably and we generate the stats on the fly later
when needed.
Use new stats in get_translation_stats function
Adapt more code to new stats
Calculate and fill in the completeness ratio used for sorting
Update spin.js to the newest version (1.3.2) + adjust its defaults