Rework of account/channel services integration

[SadieCat]

Currently services integration is very messy and doesn't allow for operation without services. This is undesirable as it doesn't allow us to implement shiny new things like distributed services.

I propose that in v4 we make the following changes:

• All of the modes other than channel and user modes r are moved from services_account to new account and channel (working names) modules
• The services_account module is renamed to services and solely handles services integration going forwards.
• The servprotect module is merged into the services module.
• The user-facing parts of the sasl module are moved to the account module and the S2S part is moved to the services module.
• Support for the IRCv3 account registration spec is implemented in the account module with the S2S part in the services module.
• A new module (name as yet undecided) is added that allows support for distributed account/channel registration and authentication without a services server.

Additionally, having user and channel modes +r seems unnecessary and their behaviour could very well be converted to user and channel metadata which would free up two valuable mode characters. That's out of scope for this though.

[SadieCat]

Having checked Anope and asked nicole about Atheme it seems that channel mode +r is not used for anything other than as a user-visible marker by modern services implementations. User mode +r does have a use ("user is logged into their nick") but this can be very trivially converted to metadata which would actually be a significant improvement as it removes the user facing -r+r spam when a user switches to their alt nick.