Flatten the list of copyright holders

It is tricky to judge the amount of work people have done here, so let's strip
out the extra spacing.
Give proper credit to Pali
Add proper credit for 3rd party software we ship

The quoted-printable & imap-modifieed-utf7 encoders and decoders, the KDE's
proxy models, the ModelTester, the FlowLayout, the mimetypes-qt4 and the
qwwsmtpclient are all shipped as a part of Trojita, so a proper credit must be
mentioned in the "accompanying documentation".