irssinotifier.pl: use perl for sending instead of wget

Running shell programs with unvalidated outside input is scary,
use LWP::UserAgent instead for sending.
irssinotifier.pl: use perl for encrypting insteal of OpenSSL

Running shell programs with unvalidated outside input is scary,
use Crypt::CBC instead for encrypting.
irssinotifier.pl: remove unneeded is_dangerous_string

is_dangerous_string is not needed as the strings are not passed to
shell command line anymore.