Changes for 0.16 release & debian compat upgrade

[jredrejo]

• Update debianization to bookworm standards
• Remove unneeded conflict with python3-markdown package

Merging it as Launchpad build has gone fine https://launchpad.net/~learningequality/+archive/ubuntu/kolibri-proposed/+build/27779419

Closes: #131

[holta]

Fantastic news, Thanks @jredrejo !

💯