Added a way to use a DOM element as the container

Hi,

I wanted to wrap qwerty-hancock as a Angular.JS directive, but there is no way to apply it to a regular DOM element instead of providing an ID. I added support for an optional setting called "element" to do something like this.

Also did some refactoring:
- Removed unused variables
- Removed the ID-parameter from drawKeyboard(), this parameter wasn't in use

I also saw qwerty's using IDs for the keys - I'm thinking about using classes to support multiple instances of the on-screen keyboard. I will create an issue. :-)

Best regards,
kpko