Setting for turning off the sharing indicators

[careck]

With the new sharing features there is now a little coloured dot in front of every note which indicates which permission you have for this note. This is relevant in a workspace which is shared between multiple peers, but can be distracting either:

1. if you're the only user and never share the workspace, or
2. if a peer has the same access on every note and a uniform colour doesn't really emit valuable information any more.

Therefore we should have an application wide setting which allows a user to choose between different display modes:

1. Sharing indicators always off
2. Sharing indicators always on
3. Only show sharing indicators once a workspace is shared with at least one peer

This is a global setting and should be in the appearance section of the global settings menu.