Replace T4 templates with PowerShell templates

Easier to add and maintain the units. No dependency on Visual Studio.

* Add powershell script and include files
* Add unit definitions in JSON with prefix support
* Delete oboslete files related to old T4 templating system

Breaking changes:
* Delete OtherUnit, move Table/teaspoon into Volume
* Rename month and year units
* Fix plural naming of
  * Pressure.KilogramsForcePerSquareCentimeterInOnePascal
  * Ratio.PartsPer-units

Other changes:
* Support custom tolerance per unit in tests
* Move code more consistently into Custom/GeneratedCode folders
* Fix misc R# warnings
* Match R# cleanup profile in generated code