refactor(locators): moves scope in locators to last argument

scope defaults to document, and is an optional argument so now be moved to the
end. Came up from debugging and trying to use
window.clientSideScripts.findInputs('username'); which failed. Refactored to
match original intent.

BREAKING CHANGE: anything relying on clientsidescripts should no longer pass
    element scope as first argument.

    Before:

    window.clientSideScripts.findInputs(document, 'username');

    After:

    window.clientSideScripts.findInputs(document, 'username');

    Also, any custom locators using addLocator will now break since the
    arguments order has chnaged. To migrate the code follow the example below:

    Before:

    var findMenuItem = function() {
      var domScope = arguments[0];
      var myArg = arguments[1];
      // balh blah blah
    };
    by.addLocator('menuItem', findMenuItem);

    After:

    var findMenuItem = function() {
      var myArg = arguments[0];
      var domScope = arguments[1];
      // balh blah blah
    };
    by.addLocator('menuItem', findMenuItem);

Closes #497
docs(debugging): Add note about limiting scope when using clientSideScripts