Make it work with cabal sandbox.

FromField Word8 is already defined. Why?!
Adds a mkNewInvoice utility function.
Cleans up the error msg (invoice details view).
Uses the new mkNewInvoice utility function.
Add Client/Address to Eq Class.
Switch to Invoice view on item activation.
Adds log text field to the invoice ui.
Adds Invoice UI Updates on setting a new invoice.