Fixes nested tasktemplates on the first level

[elioschmutz]

This PR fixes the initial state of tasks created from a task template.

To make it clear what really changes through this PR, the first commit provides a bunch of missing tests of the current implementation which will then be updated with the bugfix.

Here is an example of what changes through this PR: If I start a process with the following structure:

• Parallel Task
  • Task 1
  • Task 2
  • Sequential Task
  • Task 3
  • Task 4

The tasks where started in the following states:

• Parallel Task (in Progress)
  • Task 1 (open)
  • Task 2 (open)
  • Sequential Task (planned)
  • Task 3 (planned)
  • Task 4 (planned)

With the fix, it would create tasks in the following states:

• Parallel Task (in Progress)
  • Task 1 (open)
  • Task 2 (open)
  • Sequential Task (in Progress)
  • Task 3 (open)
  • Task 4 (planned)

Before

After

For TI-1300

Checklist

Everything has to be done/checked. Checked but not present means the author deemed it unnecessary.

• [x] Changelog entry
• [x] Link to issue (Jira or GitHub) and backlink in issue (Jira)