Misc tasks

[amartinhuertas]

cc @fverdugo

• Upgrade dependency versions. (Gridap 0.17) PR Upgrading to Gridap 0.17 #36
• Rename PETScSolver by PETScLinearSolver. PR Renaming petsc linear solver #37
• Add support for SNES. Wrap it around Gridap NLSolver implementor. PR Adding snes support #38
• Implement Garbage Collector in the spirit of issue Discussion on GC of PETSc objects on PETSc-Users #41
• Use convert API to transform from PartitionedArrays to PETSc and vice-versa. Done in PR Adding snes support #38
• Investigate the interplay among GridapPETSc.with(...) and PArrays.prun(). See also PetscLinearSolver partitioned mpi support #46 (comment)
• Something else?