Revert "Completed a bunch "lessons""

This reverts commit e9d970d4f0a8a597ab60b0d19b9d15e293cd2bd4.
Completed a bunch more of the koans "lessons"

AboutBooleanLiterals.scala
AboutLiteralNumbers.scala
AboutLiteralStrings.scala
AboutTypeSignatures.scala
AboutTypeVariance.scala
AboutUniformAccessPrinciple.scala