HistoryMatch: Misfit improvements

Future frontend/Dash component improvements include:
- Add a "guided tour" to the plugin (as already added for some other plugins), explaining the user what he/she is looking at (especially the confidence intervals in the background, indicating areas of overfitting/underfitting, might be a difficult concept).
- Move legend out of the plot. Visualize axis ticks better on small screens.
- Option for showing total misfit per group (i.e. contribution in the misfit function), and not only average misfit within a group (as now).
- Observation type aggregation (currently it is one bar per "obs. group/key", e.g. `WOPR:A-1H`... would perhaps be useful to easily be able to aggregate this such that you show average/total normalized misfit for `WOPR:*` as a total, and `Rates` (`WOPR`, `WGPR`, `WWPR` etc.) as a even higher aggregration level).
- When hovering over a misfit bar, it could "dissolve" into the different "realization points" (a technique also used in the Parameter Distribution Plugin) - enabling the user to easily identify realizations with good/bad match wrt. to a given observation type.