Use T4 templates to generate unit code

[angularsen]

This has been on my wishlist for some time. Started a T4 branch today and got a lot of good stuff done.

It's quite a big task and refactoring, but it will greatly simplify adding and managing the units and constants. I've currently got Force, Length and Mass working, the rest should come soon. I expect to be ready to merge into master this week.

[angularsen]

https://github.com/InitialForce/UnitsNet/tree/T4

[angularsen]

Fixed in v1.10.
https://github.com/InitialForce/UnitsNet/tree/v1.10

[angularsen]

UnitConverter is now also generated by T4.
The only remaining now is to generate big parts of the test code, creating a separate issue for that.