Rewrite/Factorize plot and image window module

[daurer]

plot and image are overloaded with features that have gradually been added. The current status of the plot window and image window module is reflected by a long list of existing frontend bugs.

Approach: Revisit the desired frontend features and build a new, more structured and modularized class for image and line plots around these features.

One could start factorizing based on the type of data sent from the backend. So far, the different data types (per event) are

• scalar
• vector
• image

which are assembled to form

• line plots (history plot)
• 1d histograms
• 2d histograms
• image stacks (buffer of hit patterns)
• line stacks (buffer of tof traces)

This needs major changes and should be done inside a separate branch and accompanied by adding test functions.