hist_seat added to layout in config file; hh_seats added to Hud.layout

Fixes a bug where iPoker and similar sites fail to display
player stats in the correct locations (and can omit players from display)
Some sites omit seat nums in hh files, e.g. iPoker
uses 1,3,5,6,8,10 - not 1,2,3,4,5,6 - in hh for 6-max, and these
non-contiguous seat numbers are stored in the fpdb db.
In config file, layout locations now have new optional
'hist_seat' attibute: if not specified in conf file,
'hist_seat' defaults to 'seat'.
Configuration module reads 'hist_seat's as hh_seats (a new list attr
for each Layout in the Hud class (e.g. [None,1,3,5,6,8,10])
Aux_Base.get_id_from_seat() returns the id based on hh_seat[seat],
  to make sure that the correct player id is obtained.
OTHER ALTERNATIVE FIXES TO THE ABOVE CHANGES:
1. amend hhc to always store contiguous seat numbers; or,
2. amend ranges creating/updataing stat windows to use
seat nums stored in db (not range(0, max+1)); or,
3. Specify hist_seat values differently in the config file
(e.g. as hh_seats="1,3,5,6,8,10", rather than each one specified in
corresponding layout location node)