Fixed cmake cpack configuration.

The licensing file variable for cpack needed one and one only file
so I chose the most used aka the GPLv2 one.

Fixes #217
Added a true 48x48 app icon for linux installations.

Thanks to anholt for pointing out and for all the rest! :)

Fixes #210
German translation update thanks to NaN :)
Added small polish on the second path part and added a veeery early version of the third part.
Decrease the forward thrust damages to better fit a larger game scale
while still doing more damages than a standard attack.
While seeing it, rewrote some ugly audio code to stop passing a pointer uselessly.

This made the thing almost unreadable.
Small typo fix.
Actually fixed the character running after battle end animation being sometimes reset to idle.
Added the new mountain battle background made by Tamara Ramsay :)
Kept on the third map part and added the new castle tileset from Zabin :)

The map is still empty but most of its tiles should fit now.
Added pch support for gcc when using cmake under linux.

Other OSes should use XCode, MSVC or C::B to compile, anyway.

I also removed the jpeg.cmake module as it is useless now,

This fixes #209
Precised the licensing of the water tileset to remove a licensing trouble.
While seeing, updated a bit the manual file.
Removed the stars from the mountain village house background to avoid a licensing problem.

Should fix issue #214.
Removed the map items art file as it was causing licensing problems.

Should fix #216.
Forgot to update the license file.
Added a few missing tiles to the castle exterior 2 tileset and fixed a bit the path3 map.
Regenerated PO file and updated Galician translation
Fixed cmake pch compilation when not builing from the top source folder.

This fixes #218 for me. Thanks to Gallaecio for poiting out. :)
Merge pull request #219 from Gallaecio/master

Regenerated PO file and updated Galician translation