Added capability for additional text fields to be added to AlertViews

[msec]

Fixes #68: Added code to be able to handle multiple textfields in an alertview simply by passing in placeholders for the desired textfields. Placeholders should be blank (@"") if no placeholder is required.

An outlet has also been provided to be able to access the value in the textfields from the block for the Done button.

There were a number of left over methods after these changes which I could not see a use for, so I have removed them to avoid clutter / unneccesary complexity