HTML popup component and popup controls

[oscarlorentzon]

With the mouse event API (which supplies basic coordinates) it is now more valuable to add a popup component API.

The popup controls should:

• Automatically adjust alignment based on position on canvas (maybe if configured)
• Allow any HTML to be inserted
• Be secure
• Have a generic design
• Be anchored to a basic image coordinate
• Stick to basic coordinate position when panning/zooming

[gyllen]

@oscarlorentzon I like this requirement, lets find a use case for it first and then implement it (it might come pretty fast with tagging moving in the pipe)