Selecting boolean should happen via dropmenu, not checkbox

Issue found:

• Selecting True/false is too difficult as the checkbox is wrong way to do this. Also, it is barely visible.

• Snapshot: 17
• OS: Mac OS/ M1

How to reproduce

1. Open Model editor
2. Create a column, and select boolean data type
3. On dark theme, the checkbox is barely visible and selecting it weird

Expected behavior

Dropmenu would work for this data type much better. 

• When a cell is empty, it shows select in the drop menu (Empty in JSON)
• When true or false is selected we show it in drop menu