Reflect supervised features relationship in the inspector's UI

[Michał Sikora]

• Indicate that a feature has a supervisor. (#119)
• Navigate to supervisor from child. This can be tricky because features can be in different tabs. (b75e380)
• Indicate what is supervised by an option. (#124)
• Navigate to child from supervisor. Same issues as above. (#124)

[Alex Krupa]

How about minimal approach for a start, e.g. supervisor feature's name in a TextView?

------------------------------
ChristmasTheme
  Determines if Christmas theme is enabled.
  Enabled    Disabled
------------------------------
Greeting
  Supervisor: ChristmasTheme
  Determines greeting type if Christmas theme is enabled.
  Hello    HoHoHo
------------------------------

[Michał Sikora]

Sure, sounds good for a start. Want to make a PR?