First version of OctoPrint with i18n/l10n support

Also included is a translation for (informal) german.

New languages can be added with "python setup.py babel_new --locale=<language code>" which will create the corresponding .po file from the existing .pot file under "src/octoprint/translations/<language code>". Translations can be refreshed from strings in source with "python setup.py babel_refresh". Existing translations can be compiled into usable translation files (.mo for python and .js for Javascript) via "python setup.py babel_compile".

 You'll need to install the development dependencies for all of this to work, just issue "pip install -r requirements-dev.txt"

 Note: numbers are not yet correctly formatted for their respective locale (e.g. "2.5mm" instead of "2,5mm" in german).