get PairTableKokkos to inherit from PairTable (also fix GPU)

synchronize pppm/cg with changes in pppm and remove block on triclinic

Fixed bug in lamda_box_corners function

Initializing pointers in neighbor.cpp

Fix nvk implemented

GitHub tutorial update

Fix momentum kokkos

Kokkos bugfixes

Update Colvars library to version 2016-12-22

USER-DPD updates

Merge branch 'github-tutorial-update' of https://github.com/Pakketeretet2/lammps into github-tutorial-update

some formatting updates and text rewrites for your pull request

forgot to extract this change when
separating the commits for PairTableRX
and PairTableKokkos.

This reverts commit aebc8ea8.

to avoid having it be replicated
in several different locations

the code was crashing when trying to
deep_copy or assign views that had
not been allocated

realize that there is a lot of copy-paste
in this codebase.

prevent implicit dereference of s_CTEMP

Any paragraph starting with IMPORTANT NOTE: is transformed into a warning.