GHContextMenuActionType (Pan / Tap)

First of all, thanks for the share - great tool!  I added a small tweak that I was wanting, and so thought I'd share.  Just adds the ability to choose how the menu item can be chosen.

```objc
typedef NS_ENUM(NSInteger, GHContextMenuActionType){
        GHContextMenuActionTypePan,
        GHContextMenuActionTypeTap
};
```
* GHContextMenuActionTypePan : this is the default (current) behavior ( pan to select a menu item )
* GHContextMenuActionTypeTap : allows the menu to be shown after the long press is triggered, but then the user can stop pressing and just "tap" the menu item.  

### Example Usage
```objc
    GHContextMenuView *overlay = [[GHContextMenuView alloc] init];
    overlay.dataSource = self;
    overlay.delegate = self;

    // using tap.  Could just create a separate initWith too i guess.
    overlay.menuActionType = GHContextMenuActionTypeTap;

    UILongPressGestureRecognizer *_longPressRecognizer = [[UILongPressGestureRecognizer alloc] initWithTarget:overlay action:@selector(longPressDetected:)];
    [self.tableView addGestureRecognizer:_longPressRecognizer];
```


### Known Issue
This doesn't do the same animation we see with the default "pan" behavior ( out of laziness honestly ).