Reposition KGModal when Keyboard is present. Fixes issue #19

This is a feature when you have textfield/textview in KGModal and want to **reposition when keyboard appears**.
This behaviour is kept **optional** as it is not may be an everyday use.
But when you need this behaviour, just use -
```responsiveToKeyboard = YES```
...and you are all set!

Note: check example to see this in action.