Fixed run.store's chmod usage to never fail

With group/other writable files and certain umask setting, simply doing
chmod -w was not enough.
BuildKit update
Fixed GUI to work with empty result dataset
Separated JSON interface to SQLite as sqlite-json
Overhauled GUI's data interface to the engine

3x-results and 3x-status (in fact, 3x-index and queue) now exposes JSON,
and GUI uses them directly without having to parse their fragile text
outputs.