DEV: patchbot: pass the branch version to the generated page

DEV: patchbot: pass the branch version to the generated page

The review page will need to exchange its state with the update.cgi
service sitting next to it, and for this it must know which branch it
covers since all branches' pages may share a directory. post-ai.sh
takes a new "-v <version>" argument and emits it as a "branch" JS
variable; when absent the variable is empty and the page will simply
not offer syncing, keeping the output standalone as today.

update-3.0.sh deduces the version from its own name (update-3.0.sh ->
3.0), so that adding a symlink with another version for a new branch
continues to work with no other change, and passes it to post-ai.sh.