Deprecate VS2013 content and update references
Deprecate VS2013 content and update references

Changed the way we talk about the image service now that VS2015+ is a reasonable default target; added a section for other relevant extensions. Also refactored the resources section to include partner program and VSMac / VSCode extensibility.
Microsoft/VSSDK-Extensibility-Samples,Microsoft/VSSDK-Extensibility-Samples,AmadeusW/VSSDK-Extensibility-Samples,AmadeusW/VSSDK-Extensibility-Samples