Extend task query to explicitly select modules

[lefou]

There is sometimes the need to select modules. Our current task query syntax is made for selecting tasks and it's not possible to select modules. Even is a task query matches a module, if that module is also a TaskModule, instead the defaultCommand is selected. There is a exception though: mill inspect allows to select modules, but the implementation looks a bit hack-ish.

I propose to add an explicit marker to the query, when a modules should be selected.

Ideas for a good marker are very welcome!

Here are some ideas:

1. A trailing : - since we already can type-select Modules with :<type-pattern>, a : without a type could be understood as "module" as well
2. A leading symbol, like : - Since we know the fact, that we only are interested in modules beforehand this has the potential to ease and speed up resolution and completion.