Dogfood build for VS2019 Preview 1.0

This is a pre-release version of SonarLint updated to work with Visual Studio 2019 Preview.

Important notes:

• the vsix in this release is only installable on VS2019 Preview (up to build 16.0.28408.50).
• it is an alpha version, so has only undergone limited testing (issues are raised in standalone mode, can bind a solution, can update a previously bound solution).

Known issues:

None so far...
... but if you find any please create an issue in this repo and label it with Area: VS2019.

We'll release a supported version once VS2019 has shipped. Subscribe to issue #780 to receive notifications.

Enjoy!