Blender Git Loki

Modify constraints user interface and usability

I have recently been preparing focal length constraints for committing to trunk but unfortunately missed BCon2, so it'll have to wait until next time. In the meantime, this commit brings the changes that were made according to code reviews and user feedback into my branch. The interface changes include:

- Constraint value inputs are now in a column.
- User interface button names have been simplified.
- The focal length camera property is not forced to fit inside the focal length constraint range. Instead, the focal length is clamped to the range when solving.
- When the constraint is not enabled, the min and max values will adjust to match the focal length camera property. This gives the user an anchor to help understand the meaning of the values.