feat($ionicPopup): allow config of stackPushDelay

```javascript
// TODO: Make this configurable
    var popupOptions = {
      // How long to wait after a popup is already shown to show another one
      stackPushDelay: 50
    };
```
complete random TODO I found allowing the user to configure their stackPushDelay during config stage of Angular. 

Converted the .factory() to .provider() 
added missing semicolons and indentation