Add support of property OctoPackProjectName

See http://docs.octopusdeploy.com/display/OD/Using+OctoPack

Without this, the nuspec and nupkg files always take MSBuildProjectName. 
The value of the property OctoPackProjectName defaults to MSBuildProjectName, thus, if no value for this property is specified in the csproj, the output files remains as before

Source/OctoPack.Precompile.targets

@@ -3,19 +3,19 @@
   <PropertyGroup>
     <OctoPackPrecompileIntermediateOutputPath Condition="'$(OctoPackPrecompileIntermediateOutputPath)'==''">$(IntermediateOutputPath)PrecompiledIntermediate\</OctoPackPrecompileIntermediateOutputPath>
     <OctoPackPrecompileOutputPath Condition="'$(OctoPackPrecompileOutputPath)'==''">$(IntermediateOutputPath)Precompiled\</OctoPackPrecompileOutputPath>
-    <OctoPackPrecompileNuSpecFileName Condition="'$(OctoPackPrecompileNuSpecFileName)'==''">$(IntermediateOutputPath)$(MSBuildProjectName).nuspec</OctoPackPrecompileNuSpecFileName>
+    <OctoPackPrecompileNuSpecFileName Condition="'$(OctoPackPrecompileNuSpecFileName)'==''">$(IntermediateOutputPath)$(OctoPackProjectName).nuspec</OctoPackPrecompileNuSpecFileName>
   </PropertyGroup>
 
-  <Target Name="GenerateOctoPackPrecompileNuSpecFile" BeforeTargets="OctoPackPrecompile" Condition="'$(OctoPackNuSpecFileName)' == '' AND !Exists('$(MSBuildProjectName).nuspec')">
+  <Target Name="GenerateOctoPackPrecompileNuSpecFile" BeforeTargets="OctoPackPrecompile" Condition="'$(OctoPackNuSpecFileName)' == '' AND !Exists('$(OctoPackProjectName).nuspec')">
     <PropertyGroup>
       <OctoPackNuSpecFileName>$(OctoPackPrecompileNuSpecFileName)</OctoPackNuSpecFileName>
       <PrecompileNuSpecFileContent>
         <![CDATA[<?xml version="1.0" encoding="utf-8"?>
 <package xmlns="http://schemas.microsoft.com/packaging/2010/07/nuspec.xsd">
   <metadata>
-    <id>$(MSBuildProjectName)</id>
-    <authors>$(MSBuildProjectName)</authors>
-    <description>$(MSBuildProjectName)</description>
+    <id>$(OctoPackProjectName)</id>
+    <authors>$(OctoPackProjectName)</authors>
+    <description>$(OctoPackProjectName)</description>
     <version>1.0.0</version>
   </metadata>
   <files>