Formtools group actions

This PR create the ability to include group actions button. Below is an example of group actions DSL in formtools grid configurations:

```
grid: {
    groupActions: [
        {
            label: 'Assign RM',
            action: 'assign/rm'
        }
    ]    
}
```
For each of the group actions defined, a router mapping is required in your application to serve the content for the URL defined in action. The content of the URL will be inserted into a boostrap modal. Below is an example of the content required.

Example here

To-do:
- [x] Add group actions support to formtools plugin
- [x] Add group actions buttons to model index template
- [ ] Group actions buttons should be hidden by default, unless a checkbox in one of the row on model index template is selected
- [ ] Render content from URL defined in group action button action to modal
- [ ] Ability to execute javascript provided in the content
- [ ] Configure modal to post form to URL defined in action