Updating CpsExtension sample to Dev 17, extending existing rule, fixes

[adrianvmsft]

• Update the project to Dev 17
• Adding rule showing how to add a custom property to a Compile item in SDK-style project
• Fixing an issue that was causing a Non Fatal Exception (NFE displayed as yellow bar) due to MEF failing to instantiate the CustomDebugger class due to using the ImportingConstructor attribute from the wrong namespace
• Adding a workaround to copy the rule files to the output folder (being skipped by MSBuild)
• Fixing an issue that was causing extra assemblies to be embedded within the vsix
• Updating documentation

[drewnoakes]

Looks great!