Fixed '::' separation in tooltips on state buttons in grid view



This fixes the '::' separated tooltips you see on the change state buttons in the grid (list) views.
![tooltips](https://f.cloud.github.com/assets/744259/692578/2a489f80-dc34-11e2-8f2a-15397c1a3f0b.png)

To facilitate this, I have added a method to the JHtml class called prepareTooltip.
This method will convert a ```foo::bar``` style string to a string ready for the Bootstrap tooltips: ```<strong>foo</strong><br />bar```.
This method can be used anywhere else now too.

#### Testing Instructions
Check all the grid views (list views, like the Article Manager, Module Manager, etc) to see if the tooltips on the state buttons are ok.