#217 Feature request: zoom behaviour

[Brian Smith]

The zoom behaviour in assign 3.0.b2 spectrum display modules is an acquired taste, and needs clear documentation since it differs from other programs that potential users are likely to be familiar with (analysis v2, PyMol, etc.) where the scrolling zooms keeping the centre of the current view centred.
Zooming is also only currently possible using the mouse - keyboard shortcuts are required.
Suggestions:
* Description for current behaviour should be specified/clarified in the documentation
* User setable preference for current or "standard" zooming behaviour (switchable with a keyboard shortcut?)
* Keyboard shortcuts for zooming (bind to ZI & ZO?). Context dependent like the mouse.

[Luca]

Added in B3