Fix VSIX version incorrectly displaying as 2.0 instead of the current RudeBuild version of 1.5
- Preliminary VS2017 support (still needs a bit of work, mostly SN-DBS needs to run vs15build instead of vs14build for VS2017)
Switched the VSIX package class to derive from AsyncPackage and do async init.
Abandon build top-level folder.
Look for latest SN-DBS build driver vs15build.exe first.
- Support for enum value VS2019 and related version changes
Add VS2019 support, but it's not complete because haven't migrated to AsyncPackage yet and thus VS by default will refuse to load the plugin.
Slightly tweak installer to hopefully ensure RudeBuild 1.4 is fully uninstalled before installing 1.5.