initial spec
Initial UI.

I think I'm still doing something wrong here...
Model cleanup. Adds Client, Invoice and Product models.

Also extended the schema.
Adds period (from,to) as well as date and due fields.
Adds addProduct view.
Adds Invoice List, adjust to new vty-ui (1.7) api
Adds Add Invoice sketch.
Adds more Add Invoice logic.
Merge remote-tracking branch 'github/master'

Conflicts:
	LICENSE
Update README