Add initial implementation of combined BC routine

Removes specfic BC routines _apply_q_bcs and _apply_aux_bcs to provide a clean
interface to boundary condtions.  Currently works with non-custom boundary
conditions.
Fix incorrect argument passing to custom BCs
Update Rossby wave example
Do not attempt to load aux when num_aux == 0
Change auxbc setting from wall to extrapolate
Change auxbc wall boundary to extrapolate
Add extra array argument to custom BC functions
Merge remote-tracking branch 'clawpack/master' into pass-aux-2-bc
Change aux bcs to extrap
Create custom wall BCs for aux

Also clean up a bit of the code
Add back special aux wall BCs
Revert back to aux wall BCs
Add support for old custom BC signatures

Also add a warning message to tell users to change their function signatures.
Improve readability and commenting of new BC routines.
Merge pull request #452 from ketch/pass-aux-2-bc

Pass both auxbc and qbc to user BC routines