Fixed T4 template errors in test project after changing MultipleOutputHelper.ttinclude.

The change to MultipleOutputHelper.ttinclude was necessary to support outputting to parent folder (using ..\..\ in path). However, this change also made environment variables such as $(SolutionDir) no longer work.

* Replaced file include paths with proper relative paths.
* Removed duplicate assembly and namespace imports.
Removed duplicate UnitConverter.g.cs.
Fixed Shared.ttinclude and GetUnitAttributeFromUnitClassName() after namespace of attributes had changed.
Removed unnecessary includes in UnitTestClass.ttinclude already covered by Shared.ttinclude.
Updated solution hierarchy for generated unit test classes to no longer be nested under UnitTestClasses.tt.
Added auto-generated UnitTestClasses.txt.
Changed extension of output from generated.cs to g.cs.
Renamed existing files.
Regenerated flow and rotational speed units after fixing bug in constants defined in both implementation and test.
Added temperature units.

Added TemperatureAttribute.
Added temperature units and modified UnitAttribute to use linear function instead of ratio.
Added TemperatureTests.cs.
Added invariant unit abbreviations for temperature units. Still missing russian. Failing test.