Support properties KEYWORD_SET and MATCH

The KEYWORD_SET property identifies the first state in the keyword set
to use as the kanban column headers.  Consider the following keyword sets:

   #+TODO: TODO | DONE
   #+TODO: REPORT BUG KNOWNCAUSE | FIXED
   #+TODO: | CANCELED

If the KEYWORD_SET property is REPORT, then the kanban column header
will be REPORT, BUG, KNOWNCAUSE, and FIXED.  If KEYWORD_SET is not
specified, the first keyword set will be used, in this case TODO and
DONE.

Use the MATCH property to restrict entries in the kanban to TODOs
tagged with the value.