Introduces Textpattern_Date_Timezone.

Dealing with timezones. Will act as backend for the
current 'timezone' class.

git-svn-id: http://textpattern.googlecode.com/svn/development/4.x@5656 2fea6a4d-a838-0410-917b-93a53c48e9d2
Examples, comments, remove leftovers.

git-svn-id: http://textpattern.googlecode.com/svn/development/4.x@5657 2fea6a4d-a838-0410-917b-93a53c48e9d2