Allow different behavior for right or left swipes (color and trigger), 

**The best way to demonstrate the point of these changes is to illustrate the final behavior:**
![swipechanges2](https://f.cloud.github.com/assets/1195174/2062939/736f32f4-8ca7-11e3-9e6e-47f619d4ec46.gif)

### Allow different behavior for left or right swipe
* Added `thirdTrigger` and `fourthTrigger` to allow different trigger point for right to left swiping (6a08db253b59272538f8d7f74e397af6c26ded72). If unset, will just use `firstTrigger` and `secondTrigger`, respectively (cae4f3e44d62dd8a6b7b152f3ef0ca7abdc8d941)
* Added `rightDefaultColor` to set a different `defaultColor` for the start of a right to left swipe. By default it will just use `defaultColor` (e35fc13d1390ded7d5cc70cd4db8009f54a659e3, fee9a6161eb27670ac5965a59483e966425ed811)

### Allow swipe cell to completion, but then continue to allow interaction
* I wanted to be able to use MCSwipeTableViewCell to add a layer of interaction "below" the cell (either for editing functions, or additional detail). 
* `MCSwipeTableViewCellModeExit` no longer allow interaction with the cell or to swipe it back to the origin
* `MCSwipeTableViewCellModeSwitch` obviously won't swipe to completion
* Added a new mode `MCSwipeTableViewCellModeHold` to enable this behavior (see the gif above)

### Add additional delegate callback that includes the state at the time of completion
* Seems like a useful argument to add to the callback method. Don't want to break existing code, so added it as an extra method

### Note about animation
* The gif above also includes changes to the animations. Those aren't generic and are not included in a pull request. If you use only an icon, everything would work fine. If you use a full width uiview, then the animation is wrong.
* If you want to accept this pull request, and I figure out a way to make the changes generic I'll follow up with another pull request