Too many tile issue

**Is your feature request related to a problem? Please describe.**
I'm concerned that in bound mode, things are going to get buggy because it's updating everytime a number changes. If a user accidentally enters a crazy number, then the ui will try and create corresponding z boxes which cause lag and crashing behavior. This will happen in any mode if users add too many tiles but seems the mose likly in bound mode.

**Describe the solution you'd like**
I think best fix would be to cap the number of z_widgets ScanPlanWidget creates. It's unrealistic for a user to want to individually tweak say over 100 tiles so maybe create a way to cap?

**Acceptance Criteria**
- [ ] prevent crashing if user has too many tiles