make fee in TransactionDetails Option, add confirmation_time field as Option

confirmation_time contains both a block height and block timestamp and is
Some only for confirmed transaction

.github/workflows/cont_integration.yml

@@ -78,6 +78,7 @@ jobs:
     name: Test ${{ matrix.blockchain.name }}
     runs-on: ubuntu-16.04
     strategy:
+      fail-fast: false
       matrix:
         blockchain:
           - name: electrum