[breaks-compat] Natural language browser config & semver

Regarding the required browsers for the campaign:

The old config properties `majorVersion`, `minorVersion` and `revision`
were removed. Instead, semver-compliant version matching was put in place.

Browser config based on verbose entries with `browserName`, `os`, version
entries and `name` for display alias, was replaced with simple processing
of natural-language string (like "Chrome 27 on Android").

Close #40.
[breaks-compat] Refactor confusing browser/browsers options

Renamed `browser` to `run-browser` to avoid confusion with `browsers`
specifying required browsers for the campaign.

Close #36.