Abandon apca check

[vincerubinetti]

Closes #22 as wont-fix. See https://github.com/StackExchange/apca-check/issues/143

• update expand/collapse icons
• remove apca-check as it wasn't working anyway
• re-enable normal/current WCAG v2 (or whatever) color-contrast rule (which is very inaccurate and not very useful), and make it a warning instead of a failure

See this issue, which might cover APCA: https://github.com/JRaviLab/molevolvr2.0/issues/33

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