added Transifex support

Transifex support includes:
 * hosting & translation of the language files at https://www.transifex.com/projects/p/MP2_CommunityPlugins/resource/webradio/
 * a script to download latest translations from Transifex via Transifex Client (tx.exe)
 * Transifex Client (tx.exe) is downloaded on demand, does not need to be added committed to the git repo
 * Line endings of language files are fixed after download through tx.exe to prevent modified files, if the actual content has not even changed
 * The English language file is updated automatically by Transifex from https://raw.github.com/BigGranu/Webradio_MP2/master/Language/strings_en.xml

More information are available at http://wiki.team-mediaportal.com/2_MEDIAPORTAL_2/8_Contribute/Localization/Translation_Guide