Add date parameter type to Macro Browser property editor

Confluence has several macros that work with dates in one way or another, and inserting correct dates via the macro browser today can be quite awkward, with the possibility of misinterpreting the date format, selecting June 31, or other nonsensical dates. Confluence should add a date picker to simplify choosing correct dates, and make this a standard part of the macro browser property editor for macros with date parameters. This will make writing new macros that work with dates easier, and make new and existing macros more robust.

To support this, the macro parameter type declaration will also need to add a date parameter type, so that macros can declare what parameters are dates.

Additionally, the date picker should support some helpful 'magic' date names, like 'now', '1 month ago', 'next month', etc. A user should be able to select these to jump around in the date picker, then select to an adjacent date to choose the date they want.