PPA: add libproj-dev to fix missing dep in Xenial
PPA: add libproj-dev to fix missing dep in Xenial

To be removed from control.in when Xenial comes to EOL, since it works 
w/o that line in all other distros.

MRPT/mrpt,MRPT/mrpt,MRPT/mrpt,MRPT/mrpt,MRPT/mrpt