Replace the old (and broken) jshint + jscsrc by eslint and configure
it to support some of the ES6 features.
The command `eslint` currently has one error which is a bug that was
discovered by its static analysis and should be fixed (usage of a
dead object).
This includes a security fix in mquandalle:bower, and a new package
for useraccounts iron-router templates which forced us to move some
configuration function calls.
