Various bugfixes from Alpha

[yeastplume]

Ongoing, addressing various alpha issues

• 80 - Don't display proof button (not generated) or slate retrieval for self spend (it's gone and posted once you've performed it) on transactionlist row

• 82 - Add explicit transaction cancel during self send, required wallet upstream fixes in https://github.com/mimblewimble/grin-wallet/pull/699

• 79 - Cancel tranaction, required wallet upstream fixes in https://github.com/mimblewimble/grin-wallet/pull/703