Unify the use of single and multi-root templates

[mkolar]

Issue:

We have two types of root setup for a project.

Single root used in the template with {root}.
In the settings it looks like this.

and multi-roots used in the templates with {root[name].
In the settings it looks like this.

This is quite complex on many levels.

Solution:

Only keep what is now multi-root system and for simple projects use root['work'] sa default. Or any other root name the studio chooses, since multi-roots implicitly support single root storage as well

[create-issue-branch]

Branch feature/1010-unify-the-use-of-single-and-multi-root-templates created!