#225 Unit Groups with tags

[Thomas Mueller]

An Idea from jaenicke: Have persistent unit groups based on tags that can be opened by selecting that tag. One idea could be to add a special comment to the top of a unit, listing the tabs, e.g.:

{GXTAGS: BLA, BLUB}

An expert could then scan all units in the project (or even the search path?) and collect the tags, and then present this data in a list (only tags) or tree (with the units a tag contains), for the user to open all at once.
Tags could possibly be nested by e.g. using a dotted notation: {GXTAGS: BLA.BLUB, BLA.BLA}.

These units could be opened in addition to or instead of the currently open tabs, or maybe in an additional editor window.