Merge branch 'release/v0.2.1' into development
New features are introduced in the README
I created several classes based on my ideas
Work in progress, something already works
Now I have speview and speview-new, so I can freely change the content still being able to compare them
Interactivity already works, but calibration isn't
Good, now we can append spectra to the plot (key "A" works)!
Well, now we can remove spectra from dataset, but it works quite ugly.
  1. We need specific color or style for current active spectrum
  2. We need to check if the line is already in dataset before we add it
Idea
----
Use spelist to create a dataset with a fixed length. Assign each filename
a label - if it is held or not. If yes, save data and plot them
I went home
Save class draft before I delete it
Well, now it works! I can add lines and remove them with hotkey. It's time to fix everything
A lot of improvements
Now the instance of color manager is not in any class
Calibration is fixed
Refactoring finished, now the program has 5 classes and is much more flexible than before
I have forgotten to include the main file into the previous commit!
Merge branch 'feature/refactor' into development
Now the line states are switched with a space bar button
Minor changes. Now the length of the labels in legend is easier to customize
Discovered and fixed bug (crash if no calibration is required)