TOOLS: Replace copyright notes with trademark notes

As per per https://github.com/xoreos/xoreos/issues/47 , the usage
of copyright notes is wrong there.
TOOLS: Remove wrong-headed copyright note

See https://github.com/xoreos/xoreos/issues/47 .
Instead, we list the trademarks in the AUTHORS now.
TOOLS: Update the copyright header

Replace "this software" with "xoreos-tools" to make it more
explicit and link to the GPL on the web instead of suggesting
to write a letter to the FSF.
TOOLS: Update the copyright header in AUTHORS too