po: fix all po headers from git-gui to git-cola

This commit updates all po headers to the project named 'git-cola',
following the gettext po format.
* Basically, s/git-gui/git-cola/g
* Copyright declaration
    * Previous contributers of git-gui translation are still preserved
    * update copyright year according to git-cola's commit history
      https://github.com/git-cola/git-cola/commits/master/po/*.po
* point Report-Msgid-Bugs-To entry to https://github.com/git-cola/git-
cola/issues
* reset all language team mailing lists since that only applies for git-
gui

Signed-off-by: Ｖ字龍(Vdragon) <pika1021@gmail.com>

Conflicts:
	po/zh_TW.po
Merge pull request #300 from Vdragon/fix_pot_metadata

po: fix all po headers from git-gui to git-cola

Signed-off-by: David Aguilar <davvid@gmail.com>
cmds: fix decode error when launching misconfigured editor

We were casting to unicode() where we were previously casting to str()
to fix a unicode decode error.

The right solution is to not convert at all and get the error
message directly from e.strerror instead.

Closes #298

Reported-by: Ｖ字龍(Vdragon) <pika1021@gmail.com>
Signed-off-by: David Aguilar <davvid@gmail.com>