XLIFF files can have multiple extensions

Add support for xliff extension in xliff files.
requirements: make min and pinned proper release time files

These are no longer stored in the repo and are to be built at release
time.  So no longer any confusion about changing these files during
normal development.

Hopefully this opens up some more testing against current and latest for
us.
static: Add a js languages file

This file will be autogenerated by make linguas once some fixes are
upstreamed to TTK.
static, templates: Add a global language picker
profile: Remove ui_lang from the profile
Don’t try to update non-existent summary

Fixes the misleading error:

  TypeError: view() got an unexpected keyword argument 'dir_path'

Which was the result of making an AJAX request with empty URL that gets
interpreted as index page view() which is not prepared for AJAX requests
(and shouldn’t).
Remove non-existent logging bit that sneaked in

Those are related to logging changes in Evernote’s fork that we did not
pick, I failed to remove those while merging which broke submitting
translation! If we decided to pick the new logging code, this commit
should be reverted.
cache: Cache the top stats for a much longer time

Previous behaviour had us cache for x*POOTLE_CACHE_MIDDLEWARE_SECONDS
which is 10-15 minutes by default. That is ridiculously quick for
something that is very expensive to compute and doesn't change that
much.
By default we now cache for a whole day and this can be changed in the
new setting TOP_STATS_CACHE_TIMEOUT.
settings: Document POOTLE_TOP_STATS_CACHE_TIMEOUT
travis: compile all Python files

Catch syntax errors early, especially in files that we might not test
during installation.
PEP8: W191 indentation contains tabs
Py26: with doesn't support multiple contexts

Unfortunately with does not support multiple contexts in Python 2.6 see
http://stackoverflow.com/a/12141070/2167584

So converted this to nested with statements which should work on all
supported Python versions.
Make this check more clearer
Partially revert "Cleanup: removed dead code"

This partially reverts commit 4df98e21be292f24f5c94b4c6b63c0accf4ffd72.

Was necessary since we want to keep open the possibility to have several
files in a terminology project.
Reverse hardcoded URLs
License cleanups
Get rid of the single quotes on HTML code
Replace hardcoded URLs with url template tag
Cleanups: multiple minor cleanups

ctx, form and model fields, imports order, shorten calls, blank lines,
remove try block, unused imports, model order, use single quotes on URL...
Use elif template tag