ES6: Merged Opera 15+ with Chrome

Since Opera 15+ and Chrome use the same JS engine, and are lockstep
with releases, it makes sense to combine the two. Fixes #153.
Marked Chrome < 35 obsolete
Updated Chrome 37 results

The latest Canary build seems to support for..of and arrows.
Feature name column is no longer dimmed

When a single feature row is selected, the other columns' names are no
longer dimmed. Fixes #128.
Obsolete browser columns are partially desaturated

New feature: when "show obsolete browsers" is enabled, the additional
columns are drawn using slightly desaturated colours to offset them
from the current browsers.
Merge pull request #176 from webbedspace/css

Some CSS changes
Merge pull request #177 from webbedspace/opera15

Merge Opera 15+ into the Chrome columns. Closes #153
Added 2 extra let tests

These tests check for the temporal dead zone, and correct for-loop
iteration bindings. They are distinct from the basic let-test, as they
represent more advanced or nuanced functionality.
Altered the TDZ test to include const

Both const and let are subject to the temporal dead zone.
Fixed a small bug

Also updated IE11 support for for-loop iteration scope.
Const test now checks that assignment is an error

Assigning to a const should be a syntax error. This commit does not
update the test results to match this stricter test, yet.

This also fixes tabs introduced in previous commits.