Only sync the wallet's output status from Base nodes that are synced to the chain tip

[philipr-za]

Once we have the ability to monitor a base node's chain tip and sync status as described in #1806 the wallet should only check the status of its spendable outputs from base nodes that are synced to the chain tip.

Currently the wallet will immediately ask a base node about the wallet's spendable outputs and if the BN doesn't know about them the wallet will consider them invalid. This could be done in error if the BN being queried is not up to date.

[philipr-za]

It is possible to ask the BN if it is synced rather than relying on multiple BN's. The support for multiple BNs will be more robust but I think that can come after this issue.