Wiki update - User Interface (+ Layout)

[Joachim Dreimann <jo...@wandisco.com>]

Over the last few days I have carried out a major overhaul of the Wiki
pages relating to the User Interface (UI).

Firstly I've added a section on Contributing Designs to the contribution guide.
https://issues.apache.org/bloodhound/wiki/BloodhoundContributing#ContributingDesigns

I've also written up some UI basics and a(n exhaustive?) list of the
different screens/views/elements the Application will contain:
https://issues.apache.org/bloodhound/wiki/Ui

An important new entry is the Layout, which describes the basic layout
of all pages:
https://issues.apache.org/bloodhound/wiki/Ui/Layout

I'm still in the process of creating and updating pages relating to
other parts of the UI that I've already prepared.

As always, all constructive suggestions are welcome!

- Joe