Extend timeline macro to support templating and filtering

[jdlrobson]

Note this is related to #1258

It would be highly useful to be able to use the timeline macro in a similar way to the forEachTiddler macro.

Sometimes it might be useful to construct timelines for a subset of tiddlers. For example a timeline of plugins:

<<timeline filter:[tag[systemConfig]] >>

Sometimes you might want to do other things such as show the modified timestamp for each timeline element, or show the SiteIcon? / modifier name. All these sorts of use cases could be met by adding a template parameter as well.

<<timeline filter:[tag[systemConfig]] template:Foo>>

where Foo is a tiddler with the text

<<view title link>> (<<view modified date>>)

would create items with a link and the modified date in brackets.

This would be backwards compatible and would provide an easy way to generate timelines of tiddlers.

Code is currently being written with tests to meet this requirement.

[jdlrobson]

a suggested rewrite of the timeline macro with backwards compatibility tests and test for new functionality