Version 0.2.0

Implemented features:

• Parse rwthonline-file and calculate relative passing limit
• Round in passing limit / max point-control to correct grade boundary, show correct number of decimal places
• More detailed control over the grading of the exam in the options
• Don't show histograms for exam parts without points
• Point histogram bucket size depends on grade boundary step size and is changeable
• UI improvements
• Add CI, unit tests and coverage analysis

Closes #59 (closed), #61 (closed), #67 (closed), #99 (closed), #101 (closed), #108 (closed), #112 (closed)