autmatic term mechanism for exercises

[Rdeisenroth]

This PR adds the functionality to set the term to auto instead of a text, and it will resolve the current term automatically:

[JeyRunner]

Looks good from my side. @FussballAndy, your thoughts?

[FussballAndy]

I would perhaps change the style s.t. instead of changing the entry of the dictionary we directly display the term and else display the value of info.term. Also the brackets around the conditions should be removed.

I.e.

if info.term == auto {
  <display term accordingly>
} else {
  info.term
}

Note that this would currently also only make auto work in the exercise subline mode, but not submission. Though #21 could anyway potentially make this note redundant.

[Rdeisenroth]

@FussballAndy done

[Rdeisenroth]

sorry it took so long, i kinda forgot about this PR. I fixed the brackets

[JeyRunner]

I will take a look next week and merge it then.

[JeyRunner]

Thanks!