Add support for double period classes

[tkon99]

For example, having maths the 7th and 8th hour results in two separate appointments.
Although I recommend making it optional.

[lesander]

Absolutely, we could merge those appointments together. I'll look into it, or do you have time for a PR?

[tkon99]

I don't have much time on hand during the next few weeks, so I'd really appreciate if you looked into it.

[lieuwex]

I guess checking the if the location and class are the same and the beginBySchoolhours have a difference of 1 will be enough.