Eeschema: Symbol editor pin table improvements

This PR adds several improvements to the pin table:

1. Pin numbers can be edited while the pins are grouped to add, remove, and change pin numbers.
2. The pin table supports changing the unit that the pin is displayed on.
3. The pin table shows a count of the number of pins in each row when the pins are grouped.
4. Extra information fields are added below the pin table to indicate duplicate pins and display the total number of pins in the symbol.

These features were built to make creating and working with symbols with a large amount of pins such as SoCs easier.