Interface: Rethink JWST and HST support

[pllim]

This was spacetelescope/pysynphot#16.

From @chanley:

Need to rethink how to support HST and JWST simultaneously. When doing a brain dead import, the default behavior reverts to defaulting to selection of tmg/tmc file by file name. Not necessarily the desired behavior (example cdbs.3000.dev will default to JWST).

From @vglaidler:

Modules that should stay in stpysynphot:

• catalog: icat functionality on $PYSYN_CDBS/grid catalogs
• graphtab: new incomplete graphtable code
• locations: where things are
• obsbandpass: things that are made from a graph table
• observationmode: wrapped by obsbandpass
• refs: globals
• spark: parser
• spparser: parser
• tables: graph and comp tabs
• wavetable: wavecat tabs

Modules that should besplit into two, so one can go into the core and the other stays in stpysynphot:

• observation: things that are made from a spectrum and any bandpass, but has special handling if the bandpass is an ObsBandpass

Modules that are used for extinction, so they might stay or might go or might need to be split depending on how this is handled:

• Cache: io intensive items, extinction and catalog stuff
• extinction: original SYNPHOT approach, deprecated but retained for backwards compatibility
• reddening: newer data-driven approach

Everything else should be core.

p/s: Also needs TEAL interface.

[pllim]

Fixed in #11 , except TEAL interface. Will open new issue for TEAL if there is really a need for that.