Remove deprecated Ubuntu; updated changelog

Closes #11 and #13.  As mentioned in #11, support for Ubuntu should
return in the future, but not explicitly.  Rather, the core of A2SERVER
itself ashould be made to run on any OS distribution for which our
requirements are met.

The goal is that any OS-specific details should be part of OS-specific
packaging or handled by the user (editing MOTD/issue files, etc.)  We
can handle those details on Debian systems because we know how to do
that when packaging for Debian.  Ubuntu, Fedora, etc. packages will have
to make their own tweaks.  This commit doesn't do all of that, but it
does mean there's one fewer things we need to worry about during the
transition.

scripts/a2server-2-tools.txt

@@ -123,7 +123,7 @@ sudo wget -q -O /usr/local/etc/a2server-aliases "${scriptURL}scripts/tools/a2ser
 grep a2server-aliases /etc/bash.bashrc > /dev/null || \
 echo "source /usr/local/etc/a2server-aliases" | sudo tee -a /etc/bash.bashrc > /dev/null
 
-[[ $(lsb_release -d 2> /dev/null | grep Ubuntu) ]] && motd="/etc/issue" || motd="/etc/motd"
+motd="/etc/motd"
 if [[ ! $(grep A2SERVER $motd) ]]; then
     echo | sudo tee -a $motd > /dev/null
     echo "Type 'system-shutdown' to turn off A2SERVER." | sudo tee -a $motd > /dev/null