[x] Disable <ActionButton> when loading prop is true
[x] Add submissionClosedCallbacks to <TransactionSender>
These are necessary because the promise returned by sendTransaction() does not reject on close of the submission drawer. This caused problems when a submit button called sendTransaction() and became disabled because if the user dismisses the dialog it cannot be opened again.
[x] Show loading indicator for tx creation in remove-trustline dialog
<ActionButton>whenloadingprop is truesubmissionClosedCallbacksto<TransactionSender>These are necessary because the promise returned bysendTransaction()does not reject on close of the submission drawer. This caused problems when a submit button calledsendTransaction()and became disabled because if the user dismisses the dialog it cannot be opened again.Closes #1227.