Support Julia built with USE_GPL_LIBS=0

[bmmogensen]

Hi maintainers,

This PR allows for including ExtendableSparse.jl in Julia and sysimages built without GPL libraries. Most notably, this removes SuiteSparse, which is naturally a dependency for several of the operations of the module.

This does not fix the inherent problems with not having SuiteSparse, but just allows us to compile a sysimage, and provided that we do not use any of the features requiring SuiteSparse, it will work fine.

Best,
Bjorn

[j-fu]

Ok thanks - I have no time to test this in sysimage building or in in the case without GPL libs, but implementation looks reasonable, so I merge.

For a replacemnent of Suitsparse I hint at Petr Krysl's Sparspak.jl. I plan to support this at least via require. Contemplating to make it the default LU factorization in then non-gpl case.

[j-fu]

BTW Pardiso is not GPL so I will remove the conditional in the test.