Updated note about Firefox and __proto__ restrictions

Correct behavior was implemented in https://bugzilla.mozilla.org/show_bug.cgi?id=1061853.
Update data-es6 as well
Fix JSHint warnings — undeclared vars, semicolons, etc.
Merge pull request #265 from evilpie/patch-3

Updated note about Firefox and __proto__ restrictions
Fixed undeclared var, and added 'use strict' to master.js
Replaced the colour strip with a coloured bar graph.

This removes the thin full-colour stripe, and instead changes the background bar-graph to use a grayed version of the colours. This avoids issues where e.g. Firefox's colour/stripe clashes with the No cells' colour.
Altered the JavaScriptCore and BESEN colour-coding

BESEN is now a brown matching its broom logo. JavaScriptCore is now a tad bluer to differentiate it from the current browser bar.