Issue 75 photo messages

Hello Jesse,

Hoping to be fine,

It was pleasure to contribute to this library, It is a well documented, code organized library.

I have finished the feature request, 

Here is my forked Repo, https://github.com/0xcodezero/MessagesTableViewController
and The branch that Containing Modifications is ' issue_75_photoMessages '

You can try the feature by yourself,
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The full characteristics,


1- The Message Data Object " JSMessage "
  - Contains the information Needed.
  - Type.
  - ... Can Add any Information ..

2- The Datasource delegate function has messageForRowAtIndexPath. retrieve the JSMessage Object.

3- The shouldViewImageAtIndexPath, shouldViewVideoAtIndexPath delegate methods are Implemented to handle show Media Message more information.

3- Video Image mask is done via category.

4- Ability to add a description text to Media Bubble, it would be shown under the media thumbnail,or  make it without description --> empty string.

5- Showing and hiding " camera Button " is done dynamically while runtime via (showMediaButton:)

6- The image Message support different aspect ratio Images/thumbnails.

7- New refactor has no special cases for iOS 7, so It would work fine with iOS6 and iOS5 if you hacked the library before.



I will be in contact, and here is my e-mail < 0xcodezero@gmail.com > if any help needed or not clear question.
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Regards,
Ahmed Ghalab