CEMirrorSymm updates

* Mirror sequence, coordinates, or both.
* Searches for CPs by default
* Display rotation axes (not always meaningful)
CEsymmGUI. Reenable prompt.

This keeps getting accidentally commented out during testing.
Fix CeSymm distanceMatrix

Distance matrices were not being stored. Now
saved and properly post-processed.
CEMirrorSymm improvements

* Inherits from CESymm not CECP, to prevent trivial alignments
* Properly set the distance matrix for reversed alignments
Removing hard-coded path.

Douglas, add it to your VM arguments instead:
    -DPDB_DIR=/Users/dmyerstu/Desktop/the_pdb/
    -DPDB_CACHE_DIR=/Users/dmyerstu/Desktop/the_pdb/