Set destination tag from dt parameter in action-send url

- Use a small timeout before setting $scope.send.destinationTag (boolean)
 and $scope.send.destination.destinationTag (value)
- Before, the $scope.watch for the other values (recipient, amount, currency) were firing
after these values were set, calling $scope.resetDestinationDependencies which would overwrite
the destination tag variables. This allows the digest to happen and the watchers to run before
setting the destination tag variables
- TODO: this is hacky and not optimal. A more correct solution would be to refactor the flow
of the send pane to avoid resetting the destination tag each time if unneeded
Fixes #862
Use angular $timeout
Merge pull request #864 from stellar/dt

Set destination tag from dt parameter in action-send url