Create generic tooltips

[vocksel]

Requirements:

• Mounts on top of all other GuiObjects
• Position it arbitrarily on the screen
• Position relative to another GuiObject
• Position relative to mouse
• Never mounts off-screen
• If the tooltip goes off-screen it will move back to the next available space

Connect it up to the Dropdown component for initial consumption

[vocksel]

Once #330 is merged we'll have access to Foundation.Tooltip which should take care of our needs