Add expected database schema version to RPCs.
- Add schema version to client code with minimum disruption to
  API surface.
- This cl is based on following cl
  https://vanadium-review.googlesource.com/#/c/13734/
- TODO to port definiton of Schema from go to js.

MultiPart: 2/2
Change-Id: I19ac4764307d65fa5811663b802a95ea94827986
11 files changed