PR #2493 introduced the new project.json schema. The tree has 118 files
with the old schema, which added several hundred warnings.
This change can't go in until PR #2864 does - it relies on those bug
fixes.
Moves CLI version suffix from preview1 to preview2
Sets channel for preview2 to 1.0.0-preview2, abandoning the Beta channel to the 1.0.0-preview1 release. Once @sokket's publishing cleanup work is complete we can re-converge the channels if desired.