Exceptions are shown on frontend #20

Description

Whenever an internal error occurs, it is shown on the website frontend.

To reproduce

Enter some incorrect input. For example, one can use inputs from these issues:

• NoSuchElementException thrown on correct CNF #17
• Alternative input header  #18

Expected behavior

Expected a more readable error message without actual exceptions being visible on the website.

Actual behavior

See issues from To reproduce step.

Environment
KoSAT website