[MIGRATED] Add user:select none wherever possible

[k88hudson]

We should add this to prevent accidental selection of elements/the copy paste menu popping up.

[Pomax]

I wonder if it makes sense to do this as a mixin, e.g.:

module.exports = {
  componentDidUpdate: function() { 
    var lnode = this.getDOMNode();
    lnode.style.userSelect = "none";
  }
}

var Thing = React.createClass({
  mixins: [
    require('unselectable')
  ],
  ...
});

Or, alternatively, set up a universal class in our LESS and wrap the classnames lib so that we can call it as:

webmakerClasses({
  ...: true,
  ...: thing.state
}, true);

and end up with the second argument determining whether text selection of content is possible or not.

[secretrobotron]

I was able to select some stuff in tinker mode a couple days ago.

[xmatthewx]

Impacts destination selector as well: #2212

[toolness]

This issue has been moved to mozilla/webmaker-core#43.
Please don't comment on it here.