Merge restrictive plugins to mod_restrict

Restricts chat, search, download and private messages.

Settings:
min_cred_use_hub ... minimum credentials allowed to search and download
min_cred_pm ... minimum credentials allowed to send private messages
min_cred_pm_op ... minimum credentials allowed to contact ops via pm
min_cred_mainchat ... minimum credentials allowed to send public messages

Default user for all of these settings.