Adds two guard clauses for events in mutators and flyouts

  - When a block in a mutator window is deselected, it triggers a workspace
    changed event that will run after the workspace has been disposed of. These
    two guard clauses are early returns if the target workspace is null.

Change-Id: I392e27d8c192e78f9f9b9982692123e239f1db20
Have ListPicker close an open keyboard when picking is done.

Change-Id: I52e5aab78a61b708412d241c871b2b8806d8a831
Add URL for non-encoded Companion for menu based download

Change-Id: I55a55ffb4b29cb670f7a1d4f32e525f80511608d