Improve regTable usability

[technofreak74]

This tool is exactly what I needed and really helped me debug some of my modbus issues, thanks for making it!

Fixes a couple of minor UI issues:

1. If you stretch the window vertically the settings tabs expand unnecessarily giving you less space to view multiple coil/registers.
2. The default/enforced width of 150 is not big enough to display the contents of column 0 on my system (Ubuntu 21.04).

Before:

After:

[technofreak74]

Thanks! 🙂