Adding `nochange` and `noposition` option to module batch processing

Currently, you can't batch copy a module if you don't select a position. That means you can copy a module with the position `none`. The help text also says 

> When copying and not changing position, it is nevertheless necessary to select 'Keep Original Position' in the dropdown

Although the `Keep original Position` doesn't exist.

This PR reimplements both options into the batch processing.

### Testing
Make especially sure you can batch copy a module
* which currently has the 'position' `none` by selecting the option `Keep original Position`
* which currently has any position by selecting the option `Keep original Position`
* to the 'position' `none` by selecting the option `No Module Position`

Of course also test if nothing from the existing functionality broke :smiley: 

Tracker: http://joomlacode.org/gf/project/joomla/tracker/?action=TrackerItemEdit&tracker_item_id=32844