panlint: Add check for features being included from outside their tree

[jrha]

i.e. one feature including a template from another

[ned21]

What the goal here? To enforce a rigid hierarchy? That seems a bit too opinionated and is not how we structure our templates, nor can I really think of any good reasons you would want to enforce that.

[jouvin]

+1. I fully support @ned21 remark. In the template library we maintain, like the grid ou cloud ones (not to speak of our local templates), we have cases where a feature depends on other features. I don't see any reason to forbid it. If you'd like panlint to check for this, I think it should be a panlint option, not the default behaviour.

[jrha]

Fair enough, I'll make it optional. We enforce a two layer hierarchy at RAL which was originally based on discussions with @gombasg I think, where the only includes that are permitted are:

• From personality/… include feature/…
• From feature/… include common/…, components/…, (+ other templates in the feature)