Implement history ui/x for senders (and receivers)

[didimitrie]

Step 0:

• I've read the contribution guidelines!

To start with, just have a simple view where one can see this stream's

• children
• parent

Also add the basic button of "save current stream as a version" (ie add to its children a current copy of the stream).

Old issue here: speckleworks/SpeckleRhino#44