Resolve "Broken Monitoring set-up"

Closes #900 (closed) Closes #885 (closed)

I fixed three closely connected issues with the monitoring setup:

1. Opening the monitoring setup, canceling it and opening it again did not correctly trigger edit mode.

• Cause was an Observable completing too early, see https://gitlab.com/recoverycat/rcc-client/-/merge_requests/773/diffs#95a0d18fe47f0d041098cb675e7a63792493a25d_151_151

2. Switching to preview mode triggered ExpressionChangedAfterItHasBeenCheckedError

• I turned some complex getters into values that get updated only when need be (since getters are prone to the above error and the same object was created 160+ times :D)
• I added ChangeDetectorRef, since ultimately some dynamic component (a querywidget) was added when an observable emitted, which can happen outside the CD-loop.

3. A faulty SymptomCheckConfig-check prevented a template from being stored at the end of the monitoring setup.

You can see the bugs on qa.hcp.recoverycat.de (for now)

1. Open monitoring setup, select template, navigate back to home; open monitoring setup again, pick template => questions are not editable
2. Switch to preview mode, check console.
3. Goto Templates (Vorlage) via main menu, click a template, switch to preview, try to save => nothing happens (check sonsole)