centralized date formats

[FND]

The attached patch adds configuration options for three different date formats, tentatively called timestamp, shortDate and longDate and using  ISO 8601-style date formats by default.

These are used in the default ViewTemplate? (as evaluated parameters) as well as in the Timeline and NewJournal? macros.

This enables users to globally define their date formats without the need to modify any shadow tiddlers.

Note:
In the  original discussion, the use of tiddler slices was suggested. However, this proved to be impractical.

[FND]

enhanced patch to use configuration options rather than tiddler slices