Add support for two-finger pan to message view container and improve

[Matthias Schoettle]

The message view container needs two-finger pan.

In addition, the two-finger pan needs a workaround to prevent scroll events. This is currently done for both structural and state views. Therefore, it would be better to move it to BaseHandler with the workaround and add a IPanListener for interested parties.

[Matthias Schoettle]

References issue #123: Moved workaround for pan and scroll events to BaseHandler. Added IPanListener and updated existing handlers that use pan events.

→ <<cset 5a87445fe5ad>>

[Matthias Schoettle]

Resolved issue #123: Added two finger pan to MessageViewContainer.

→ <<cset 58417fcc4283>>