Adding the possibility to use multiple language backends of tesseract.

Defining a new setting TESSERACT_CLEANUP_LANGUAGE for configuration of the
cleanup language file to use. Tesseract itself can use multiple
backends.

(cherry picked from commit b23c4bd833f61768faac4d2b4ca7957a0705e4ea)
Merge pull request #73 from mbehrle/feature/ocr_de

Adding the possibility to use multiple language backends of tesseract.