Bug 13899: Changing license to GPLv3

Bug 13899: Changing license to GPLv3

koha-qa should be good :

 OK	misc/devel/coverage.pl
   OK	  critic
   OK	  forbidden patterns
   OK	  pod
   OK	  valid

 OK	C4/Installer/PerlDependencies.pm
   OK	  critic
   OK	  forbidden patterns
   OK	  pod
   OK	  valid

Signed-off-by: Bernardo Gonzalez Kriegel <bgkriegel@gmail.com>
No koha-qa errors.
Test plan not explicitly stated,
script run and generates a lot of data :)

Signed-off-by: Kyle M Hall <kyle@bywatersolutions.com>
Signed-off-by: Tomas Cohen Arazi <tomascohen@gmail.com>