UI to alert of respend attempt affecting the wallet.

Transactions (respends) that conflict with transactions already in the
wallet are added to it.  They are not displayed unless they also involve
the wallet, or get into a block.  If they do not involve the wallet,
they continue not to affect balance.

Transactions that involve the wallet, and have conflict transactions
(respends), are highlighted in red.  When the conflict first occurs, a
modal dialog is thrown.

This commit removes the recently added CWallet::SyncMetaData.  It was
hiding information and making it impossible for the user to figure out
what is going on.  I may have missed some reason that it is necessary
though.