New fields and parameters

- Added 'color_states', 'text_sortable', 'slider', 'gfonts', 'bg_bundle' fields. 
/* - Added 'direction' parameter to 'color_gradient' (Horizontal / Vertical). > ignore this one, validation on color field screws the direction param, needs to be added as a new field */
- Added 'number' parameter to 'text' field.
- Added 'next_to_hide' parameter to 'checkbox_hide_below' to set how many (next) fields you want to hide.
- Added 'switch' parameter to 'checkbox_hide_below' so it looks like a switch, like the other checkboxes.
- Added 'multiple' parameter to 'post_type_select' to be able to choose more than 1 post type.
- Added 'safe_fonts' parameter to 'gfonts' field.

## Color states:
![screen-2013-01-08-4 54 09 PM](https://f.cloud.github.com/assets/1606655/51195/cf7644d2-59c4-11e2-89af-7b6f6f6b695e.png)

## Text sortable:
![screen-2013-01-08-4 36 28 PM](https://f.cloud.github.com/assets/1606655/51145/9ba34b88-59c3-11e2-8e0c-5faf858cc3ec.png)

## Slider:
![screen-2013-01-08-7 15 45 PM](https://f.cloud.github.com/assets/1606655/51651/9dc0f0ea-59d8-11e2-89c5-936bdabd704c.png)

## Gfonts:
![screen-2013-01-08-4 43 01 PM](https://f.cloud.github.com/assets/1606655/51147/9bc2c472-59c3-11e2-9ee0-9eeab08e6bb9.png)

## Background bundle:
![screen-2013-01-08-11 23 02 PM](https://f.cloud.github.com/assets/1606655/52328/7c1de3a8-59fb-11e2-8502-c5c60c0de74d.png)

## Color gradient with 'direction' => true: (to be ignored, validation screws the direction value storing)
![screen-2013-01-08-4 45 21 PM](https://f.cloud.github.com/assets/1606655/51148/9bc0fed0-59c3-11e2-9db8-701024c518d1.png)

## Text with 'number' => true:
![screen-2013-01-08-4 42 40 PM](https://f.cloud.github.com/assets/1606655/51146/9ba356dc-59c3-11e2-8864-7942d32d5769.png)

## post_type_select with 'multiple' => true:
![screen-2013-01-08-9 46 37 PM](https://f.cloud.github.com/assets/1606655/52129/c60d52e0-59ed-11e2-8884-042ae04617da.png)

## gfonts field with 'safe_fonts' => true:
![screen-2013-01-09-1 03 59 PM](https://f.cloud.github.com/assets/1606655/53592/f988cfc0-5a6d-11e2-93ed-811a49238ad5.png)