Resolve "On expenses the 6 month time range should be named "Semester""
Closes #435 (closed)
https://trello.com/c/qQIoTveb/148-on-expenses-the-6-month-time-range-should-be-named-semester
Instead of "1. Dez - 31. Mai 2018" it should be named "1. Semester 2018" Instead of "1. Juni - 31. November 2018" it should be named "2. Semester 2018"
This is important for the views but especially relevant for the generated expenses PDF.