Added 'formats' option.
Added 'formats' option.

Allows the user to specify which date formats are available allowing all
jsGantt values.  For example, `formats=hour|day|week|quarter`.  Default
is `day|week|month|quarter` as before.

git-svn-id: 2159781fc7c14c6bdd1f7e265daf7a25099c31e7@10507 7322e99d-02ea-0310-aa39-e9a107903beb

trac-hacks/trac-jsGantt,trac-hacks/trac-jsGantt,trac-hacks/trac-jsGantt