Fixes for group elements

Hi all, 

This merge contains:

- Adding multiple groups to options pages enabled by switching the id selector to class selector in groups.js
- Framework modified to localize the subfields of groups
- Framework modified to set default values for subfields of groups
- Added an local availability check to slider.js, spinner.js to check if it's values are defined in redux.slider or redux.spinner, without it, the page stops loading because of an javascript error
- field_group.php file mostly modified to support array like tree structure. The field id's inside this group will be modified as "field-id-[group number]". So when you are checking the $redux_demo variable, you'll see "-[group number]" appended to your id's, because in multiple groups, html doesn't allow same id's on different elements.

it's a beta version for #679 and #688 so needs some testing.