Support for old Panasonic .RAW files

Code and camera definitions to support old Panasonic .RAW files. Apparently these files come in three possible encodings. A simple unpacked 12Bit format, a packed format with a control byte every few pixels, and the same packed format as the RW2 files. This code supports all these types of file. Camera definitions are added for all the cameras available on rawsamples.ch. Any other cameras or raw formats (16:9, 3:2, 4:3) can be added by just editing cameras.xml as normal.

This code has been merged and verified to be working in darktable's git master.