Fix issue 1183: add indication of active workspace to project outline

[SchweizS]

Changes:

• Added indication of active workspace
• added icon to select active workspace in project outline

Todo:

• localization

#1183

[andreeis]

The icon might not be the most relevant for the "change active workspace" operation. We would prefer 'gear' first, then if not possible the 'utility' icon. If you already tried other icons but got blocked in any way so you had to pick as a last resort the current (build like) icon then let us know and we will try to figure out. If you didn't try yet, please push another commit using one of the two recommended icons.

[SchweizS]

i switched it to gear.
i just copy&pasted that part and forgot to change the icon to a better one.

[SchweizS]

localize('workspace.active', 'Active Workspace');
localize('workspace', 'Workspace');

those to keys should probably be added to the localization (tree.ts lines 461/463)