HaikuDepot: LinkedBitmapView derived from BitmapView

Sends a BMessage when clicked and enabled, shows the link cursor
when hovered with the mouse.
HaikuDepot: Added TODO to LinkView and bugfix.

SetViewCursor(NULL) does not unset the view cursor.
HaikuDepot: Use a LinkedBitmapView for the screenshot.
HaikuDepot: Paragraph: Fixed typo in PrintToStream()
HaikuDepot: Added rudimentary screenshot window.

Clicking the thumbnail in the package info area will now open a
window where the full-size screenshot is downloaded and shown. There can
only be one such screenshot window open. Navigating between multiple
screenshots of a package is not yet implemented. Also, no caching, but
this may be OK as it is, since one usually looks at these only once and
doesn't want the harddrive filling up with screenshots.