Set ignore_unconfirmed to true on the UI code

Currently the UI creates transactions with `ignore_unconfirmed` set to `false`. It would be better to create them with `ignore_unconfirmed` set to `true`, but to avoid extra work and possible errors this change should not be made before solving https://github.com/skycoin/skycoin/issues/2184 and using the changes added in https://github.com/skycoin/skycoin/pull/2183 to create transactions with the hardware wallet.

When making this change it is very important to test how the API responds when trying to create a transaction while there are pending transactions. The tests should include what happens when there are enough unspent outputs outside the unconfirmed pool and what happens when there are not enough.