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.
`HARDWARE_512MB_RAM` is in there twice.