Datepicker: Fix code style issues
Datepicker: rename select method to _select

Make select() a private method as it's not part of the specification.
Datepicker: Use short instead of abbreviated format for table header

Revert to old behavior with two instead of three chars.
Fixes layout issue with wrong day table cell width.
Datepicker: remove unneeded default setting of option dateFormat
Datepicker: fix populate alternate field demo
Datepicker: Fix icon trigger demo