Add hotkey shorcut click element in directive. close #197

[AbraaoAlves]

Allow use hotkey like this:

<!-- Press "ctrl+q" to trigger click and 'doSomething()' -->
<button ng-click="doSomething()" hotkey="ctrl+q"> 

<!-- If element is disabled, handler is not triggered -->
<button ng-click="doSomething()" hotkey="ctrl+q" ng-disabled="expression"> 

[note]: this PR put event.preventDefault in click event, assuming that ng-click is present. Fixes #197

[javisperez]

+1