Minor fixes and faster apologies

"Minor" in physical representation, "major" in spirit. - person coping with writing code after a while

Was adding a single word sorry, but discovered a few bugs on the way:

 val myCorrectTheorem = Theorem(() |- P(x)) {
   sorry
   showCurrentProof()
 }
 show

sorry simply expands to have(thesis) by Sorry, which is a handful to write when I'm washing my hands free of responsibility for a proof.

Fixes: ✏ sequantable to sequentable because I saw it somewhere ⚙ calling show on theorems now checks for sorry usage and prints with a different colour, same as the default theorem printing ⚙ showCurrentProof was failing as it relied on Theorem.repr, which raises a null exception. Changed to use prettyGoal