Detect adblockers for good, not evil

[ardgedee]

Browser extensions like Ghostery, uBlock, etc. will interfere with benign site functions like Square transactions.

This ticket proposes to detect when a blocker is used (either passively -- eg, noticing whether Square's iframe renders -- or actively -- deliberately performing an action that triggers most blockers to see if one responds) and throw up a notice explaining that the blocker will interfere with the action the user is trying to perform, and provide instructions for how to whitelist mltshp.com (and/or relevant affiliates like Square) without affecting the blocker's behavior anywhere else.

[jxyzn]

Anecdotally noting that I had no problems with signup or Square using uBlock Origin.