valid latitude checks for areagraphs.csv & fullcustom.csv

[yakra]

• fullcustom.cpp checks for unrecognized region codes, but not unrecognized system codes.
• system
• multisystem
• multiregion
• area: check for out-of-bounds lat/lng

[yakra]

The first 4 items were duplicated in #594, which was closed in #607.

• area: check for out-of-bounds lat/lng

• lng: No harm no foul so like whatever.
  Might not actually pick up points within "normal" range, -180 -> +180. Fix.
• lat: No crashes, but latitude can't be > 90 or < -90. So fix it!