Improve vsite parallel checking

Improve vsite parallel checking

The vsite struct now stores internally whether it has been configured
with domain decomposition. This allows for internal checks on valid
commrec, which have now been added.
The vsite constructor now initializes to atom range to invalid values,
so we can check that the thread splitting has been called before
constructing. This would have caught bug #2257.
Removed the vsite struct from the global construct function argument
list, which simplifies the vsite code in several places and
fixes #2257.

Also some general clean-up: removed some snews, added some camelCasing
and doxygen documentation.

More renaming would be beneficial, but should be a separate commit.

Change-Id: I467ec8b8ebfa0da090d4ac0a1d096ad9fab87eb5