Kokkos bugfixes

fix USER-OMP bug on per-atom data with hybrid styles

warning fixes (Kokkos+CUDA)

Fix skip with ghost issue

USER-DPD: Possible uninitialized variable in pair_exp6_rx.cpp bugfix.

this structure gets put inside a DualView,
so these members need to be able to execute
on the GPU

the compiler pointed out that
boundary[2][2] doesn't exist.
If I understand this correctly,
those checks should be against
boundary[*][0].

this #ifdef adds a return statement
for little endian machines, but leaves
the old one, which the compiler comlains
is unreachable. this commit combines
the conditionals so we can use #else

Added explicit initialization (to zero) for several variables inside the
inner j-loop to avoid using them uninitialized or from prior iterations
within rmOldij_12 == 0.

collected fixes and improvements

Kokkos fixes

USER-DPD another zero compute optimization

This relates to commit 4eb08a58 that was applied to pair_dpd_fdt_energy

Added source code and documentation for USER-CGDNA

USER-DPD: Skip a0*stuff computations, if a0 was set to zero in pair_coeff

USER-DPD: bugfix for a segfault when using MOLECULE and DPD together.

This saves around 10% of the runtime for many of our tests using SSA.

Fixes for srp example

Neighbor fixes