generalized 'firstChars', and some refactoring towards point-free style

generalized firstChars:
`firstChars :: [String] -> [Maybe Char]`

use firstCharsOrElse instead of firstChars which takes a replacement character

some other refactorings for more concise code with point-free function composition
Ich fürchte, das ding hier versteh ich nicht. appendMaybeHead fügt den akkumulator a an das nach Maybe String konvertierte liste an?