add translations/tiled_zh_TW.ts, Tranditional Chinese language translation
tmxviewer: Support staggered maps
tmxviewer: Added error handling

* Print out the error message
* Don't crash when the map failed to load
Merge pull request #677 from yehnan/master

add translations/tiled_zh_TW.ts
Make sure the new Traditional Chinese translation is released
Removed a superfluous snippet from libtiled.pro

This snippet was already included from tiled.pri.
Removed unused function
Merge remote-tracking branch 'bjorn/master'