doveadm: Deliver remote logs over doveadm socket

doveadm: Refactor server/client code to support versioning properly This way we can distinguish between old and new server side

doveadm-server: Refactor connection handshake and authentication Simplifies next change

doveadm: Add i_strccdascmp() This comparator considers camel case==camel-case==camelCase. This is to help with HTTP API to make it more flexible.

Changed type of internet port values to in_port_t everywhere. Created special SET_IN_PORT setting type for internet port values. Created net_str2port() for parsing internet port values. Removed several atoi() invocations in the process.

doveadm: Improved deciding whether to use TCP or UNIX socket for a given name.

doveadm: When connecting to doveadm socket without :port, use doveadm_port setting.

doveadm: Added client/server architecture support for running mail commands. This is done when doveadm_worker_count is non-zero.

doveadm: Code cleanup: Moved some functions to doveadm-util.[ch]