1. update dates 2013 -> 2013
2. add exchange history. From NO3M, modified by N4OGW to put
history functions in new class History:

Call History enable/disable, Call History filename, append call
history on-the-fly during contest enable/disable under Contest Options
dialog.

Call History can be updated from entire current log under File->Update
History from Log (useful to build history from old logs using Cabrillo
import in so2sdr)

Call History:

-SQlite database file

-File and database structure automatically created if history filename
does not exist

-History fields match exchange field types of so2sdr:
General,DMult,Name,State,ARRLSection,Grid,Number

-The same history file can be used for multiple contests, updates only
change exchange fields related to current contest log, other fields
remain unchanged (ie from other contests).

-Only valid exchange fields for current contest log are used for
pre-fill.

Caveats:

-If contests share the same exchange field (ie. DMult), and have
different information for that field, a different history file must be
used.