Show Last Cached Receive Address On Receive Screen Until Address Discovery Completes

[apbendi]

Issue 5.1

While address discovery is going on, show the last calculated & cached received address, to avoid this being empty. On first load, i.e. empty cache, I guess this should immediately show address[0]?

Possible pending: investigating if there is another way to do this that doesn't risk accidental address reuse.

[ey51]

Address reuse should be avoided.
This might become a non-issue once slowness of kasparov initial data fetching is resolved, so I suggest to defer any action on this until then.