RFE: CASTp pocket browser

[Elaine Meng]

The Chimera GUI that lists the pockets and can be sorted by volume, surface area, number of openings, etc. and then display the surface of each one as it is clicked is extremely useful. There is already a ChimeraX python example to simply read the files from CASTp and name the sets of atoms that line the respective pockets, which helps, but is less useful. Here is the example: <​https://rbvi.github.io/chimerax-recipes/castp/castp.html>

So perhaps this ticket has two parts:
(1) put the capability in the example into ChimeraX
(2) further enhance to interactive GUI similar to that in Chimera

Note that these files can be obtained from a database of precalculated results <​http://sts.bioe.uic.edu/castp/index.html?2cpk> (even though the Download help balloon annoyingly says "files for Pymol") as well as produced by a new webserver calculation on an uploaded structure <​http://sts.bioe.uic.edu/castp/calculation.html>