Drop urllib dependency, use QUrl.toPercentEncoding instead of urllib.quote
Exclude socket module again, since it was only needed by urllib
Merge pull request #200 from zas/percentenc

Drop urllib dependency.
According to @JonnyJD, it saves around 250kb in win .exe.
transifex.net is deprecated, use transifex.com instead

http://support.transifex.com/customer/portal/questions/1160404-improve-ssl-security-for-transifex-net
tx client is giving a message about it too

Also add translation type 'PO'.
Merge pull request #201 from zas/transifex_update

transifex.net is deprecated, use transifex.com instead
Name upgrade functions after full version
Ensure each upgrade function is run only once
Move variable near where it is used
Define _s once in parent function
config.setting -> _s in upgrade_to_v1_0_0_final_0() too
Add FIXME about broken upgrade hook
Make ConfigUpgradeError message more useful including traceback
version_to_string(): be smarter and accept list with strings
Simplify hook registration by detecting upgrade hook functions
Add a comment about adding an upgrade hook
Add missing % character escaping
Setup gettext before _upgrade_config() call
Move upgrade message boxes to _upgrade_config() instead of MainWindow

Re-format messages so they wrap nicely.

Remove related FIXME
Move upgrade code to its own file, no need to be a Tagger method
Log explicit messages for config upgrades and drop now useless comments

Use log.info() instead of log.debug() as it is useful for any user to know
config options were modified.