adds print_topic_on_join and print_url_on_join booleans under lookandfeel

[titibandit]

Suppresses the automatic printing of a channel's topic and/or url upon joining.
Right now, changing print_topic_on_join using /set won't register the change before a restart, since changing the variable doesn't add or remove the function call that already attached to the signals.

It's a pretty simplistic patch in its current state.

[titibandit]

Does anything speaks againt merging this PR?

[ailin-nemui]

hi, I'm sorry for letting your patch hang here like this. Many thanks for the contribution.

In its current state, it is too simplistic to be admitted into Irssi as is (it needs to work without restart and unbinding of signals) and I also need to verify if these numerics are only used on join or maybe also come from some other commands.