Implement linking support for all BaseCartesianData subclasses and fix bugs that caused hanging in image viewer

[astrofrog]

This is an attempt to implement linking for all BaseCartesianData subclasses and making sure the fixed resolution buffer calculation works for these.

TODO:

• Any required updates to documentation
• Document in code the internal use of component objects even though those aren't in the public API
• Investigate slowdown (happens even with older Matplotlib versions)
• Make sure that we re-instate support for pixel<->world linking for datasets that use this
• Check that things work properly in a real-life test

[astrofrog]

Seems to work ok but noticing some slowness in the UI which usually indicates an infinite loop of some kind, so will investigate

[astrofrog]

Here is the example script I am using for now: https://gist.github.com/astrofrog/5961aaa7f4fb3fa05c6f411b7b819a0f

[astrofrog]

This incidentally solves two long-standing bugs which caused (under certain conditions) infinite loops in redrawing in the image viewer, hence why it is labelled as Bug in addition to Enhancement.