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.

Author: angularsen

Tests/Generated Code/Includes/UnitConverterTests.ttinclude

@@ -6,7 +6,7 @@
 <#@ import namespace="System.Collections.Generic" #>
 <#@ import namespace="UnitsNet" #>
 <#@ import namespace="MoreLinq" #>
-<#@ include file="$(SolutionDir)\UnitsNet\Generated Code\Includes\Shared.ttinclude" once="true" #><#+
+<#@ include file="..\..\..\Src\UnitsNet\Generated Code\Includes\Shared.ttinclude" once="true" #><#+
 
     private void GenerateUnitConverterTests(Dictionary<Unit, UnitAttribute> unitToAttribute)
     {

Tests/Generated Code/Includes/UnitTestClass.ttinclude

@@ -6,8 +6,8 @@
 <#@ import namespace="UnitsNet" #>
 <#@ import namespace="UnitsNet.Attributes" #>
 <#@ import namespace="UnitsNet.Extensions" #>
-<#@ include file="$(SolutionDir)\UnitsNet\Generated Code\Includes\MultipleOutputHelper.ttinclude" once="true"#>
-<#@ include file="$(SolutionDir)\UnitsNet\Generated Code\Includes\Shared.ttinclude" once="true" #><#+
+<#@ include file="..\..\..\Src\UnitsNet\Generated Code\Includes\MultipleOutputHelper.ttinclude" once="true"#>
+<#@ include file="..\..\..\Src\UnitsNet\Generated Code\Includes\Shared.ttinclude" once="true" #><#+
 
     private void GenerateTestClass(Type unitAttributeType, Manager manager, string className, Unit baseUnit)
     {

Tests/Generated Code/UnitConverterTests.tt

@@ -1,9 +1,7 @@
 <#@ template debug="True" language="C#" hostspecific="True" #>
-<#@ assembly name="$(TargetDir)UnitsNet.net35.dll" #>
 <#@ assembly name="System.Core" #>
 <#@ import namespace="System.Linq" #>
 <#@ import namespace="System.Collections.Generic" #>
-<#@ import namespace="UnitsNet" #>
 <#@ include file="Includes\UnitConverterTests.ttinclude" once="true" #>
 <#@ output extension=".g.cs" #>
 <#

Tests/Generated Code/UnitTestClasses.tt

@@ -1,16 +1,6 @@
 <#@ template debug="True" language="C#" hostspecific="True" #>
-<#@ assembly name="$(TargetDir)UnitsNet.net35.dll" #>
-<#@ assembly name="System.Core" #>
-<#@ import namespace="System.Linq" #>
-<#@ import namespace="System.Text" #>
-<#@ import namespace="System.Collections.Generic" #>
 <#@ include file="Includes\UnitTestClass.ttinclude" once="true"#>
-<# 
-// This causes a duplicate definition error because UnitClass.ttinclude also includes it: 
-// @ include file="MultipleOutputHelper.ttinclude" once="true" #>
-<# // Disable output of this file, note this causes a build warning #>
-<#@ output extension="/" #>
-<#//@ output extension=".cs" #> 
+<#@ output extension=".txt" #> 
 <# 
 
     var m = Manager.Create(Host, GenerationEnvironment);
@@ -25,4 +15,4 @@
     }
 
     m.Process(split: true);
-#>
+#>

Tests/Generated Code/UnitValueTests.tt

@@ -1,10 +1,5 @@
 <#@ template debug="True" language="C#" hostspecific="True" #>
-<#@ assembly name="$(TargetDir)UnitsNet.net35.dll" #>
-<#@ assembly name="System.Core" #>
-<#@ import namespace="System.Linq" #>
-<#@ import namespace="System.Collections.Generic" #>
-<#@ import namespace="UnitsNet" #>
-<#@ include file="$(SolutionDir)\UnitsNet\Generated Code\Includes\Shared.ttinclude" once="true" #>
+<#@ include file="..\..\Src\UnitsNet\Generated Code\Includes\Shared.ttinclude" once="true" #>
 <#@ include file="Includes\UnitValueTests.ttinclude" once="true" #>
 <#@ output extension=".g.cs" #>
 <#