Highlight task patterns (=reused tasks) in the task structure editor

For a project we will probably need task patterns. For this, we are planning to use the reuse plugin and just take reused tasks as task patterns. An additional requirement of these task patterns is to have them in a different color (e.g. blue) than all the other tasks (green).

Since we are using the reuse plugin, each task pattern has already a reuse specification, with which we can easily distinguish them from the other tasks. We only need to check for these specifications while creating/drawing each task and changing the fillcolor in case of such a reuse spec.