Add new feature flags - mobileid, precompile_asmjs, hardware_512mb_ram (bug 1097428)

https://bugzilla.mozilla.org/show_bug.cgi?id=1097428

Code to use buchets in reviewer tools is removed because it doesn't work properly anyway, as feature detection of privileged APIs doesn't work in the browser.
Wasn't aware we had this. Yeah, it sucks, but as long as we have no reliable way of detecting features that's just useless.