Added method to generate the check-all checkbox in grids

http://joomlacode.org/gf/project/joomla/tracker/?action=TrackerItemEdit&tracker_item_id=31214

Added method to generate the check-all checkbox in grids

So all occurrences of:
```
<input type="checkbox" name="checkall-toggle" value="" title="<?php echo JText::_('JGLOBAL_CHECK_ALL'); ?>" onclick="Joomla.checkAll(this)" />
```
have been replaced by:
```
<?php echo JHtml::_('grid.checkall'); ?>
```

The method accepts values to overrule the default input name, tooltip (title) and onclick action.
So this is possible - but isn't necessary in any core code:

```
<?php echo JHtml::_('grid.checkall', 'my-toggle', 'MY_TEXT_STRING', 'myJavascriptFunction()'); ?>
```

Also the method adds a Bootstrap tooltip, instead of relying on the browser handling of the title.

### Testing Instructions
Check all the grid views (list views, like the Article Manager, Module Manager, etc) to see if the check all checkbox in the table header still works.
The difference you are supposed to see is that the checkbox now has a bootstrap tooltip with 'Check All' (or the equivalent in your language).