Some tweaks to the 'no compatible toolchains available' error message and the display names of the tool chain implementations.
Extracted a common interface out of ToolChainAvailability and VisualStudioLocator.SearchResult to represent some general-purpose result of searching for some tool.

- Tweaked the formatting of the 'could not find visual studio install' message.
Added @HasInternalProtocol.
Added another story.
Fleshed out some stories.