Second attempt: Major update

[fkuschel]

Implementation of:

• new data structure: multiple input sets in one pd.DataFrame()
• polarization curve calculation
• variation study
• save/download and load local results

Closes #19

Tasks

• [x] combine commits
• [x] check requirements.txt / environment.yml
• [x] clean ui-plot figure correctly
• [ ] check compatibility with cloud services (ServersideOutput, Redis,...)
• [ ] adjust progress bar (don't write local progress file)

[lufire]

I changed styling of code and a few layouts a little bit, and resolve a merge conflict somehow. Please review that I didn't break anything.

[fkuschel]

Checked!