Meta: Make distributed deployments possible

In the light of #277 and Project Hexanet's internal needs. Here is the list of things to do:

- [x] #259

Refactoring:
- [x] #303
- [x] Replace updatepipe package written for go-imap v1 with a better update dispatcher.
- [ ] Implement support for some distributed broker - to be used with IMAP updates distribution.
- [ ] #262.
- [x] #304

Several queries should be optimized/reworked in go-imap-sql in order to behave well in a distributed environment:
- [ ] https://github.com/foxcpp/go-imap-sql/issues/28
- [ ] https://github.com/foxcpp/go-imap-sql/issues/33

Officially support CockroachDB:
- [x] https://github.com/foxcpp/go-imap-sql/issues/5
- [ ] Officially support CockroachDB use with auth.sql_table/auth.sql_query.

In other words, we have a long way to go. :)

Comienza revisando los elementos completados y pendientes de este issue, especialmente #277, #262, #303, #304 y los issues 28, 33 y 5 de go-imap-sql. El trabajo abarca un dispatcher de actualizaciones, compatibilidad con brokers distribuidos, el comportamiento de Distributed SQL y la compatibilidad de CockroachDB con auth.sql_table/auth.sql_query; se considera terminado cuando los requisitos de deployment relevantes que aún no están marcados se hayan implementado y sean oficialmente compatibles.

Escrito por el modelo de indexación a partir del texto del issue.