ECMPoQmTools: Add option to skip processing of po files

This will cause noise and CPU overhead on incremental builds. Especially with make it is quite a bit slower. On my local setup I don't need/want the translations to be installed anyway. Especially with projects having few targets, this speeds incremental build up by a large portion. This should not be relevant for packaging, but due to the little complexity of the new option I consider it a nonissue.