Those version numbers are now also stored in the binary, making sure it is recompiled
when a new version of an extension is used. This avoids updating the binary version
for minor changes to extensions and also makes this work for plugins.

- Added sieve_global_extensions setting.

Made vnd.dovecot.debug extension available to the LDA plugin instead of only the command line tools.

Imap4flags: added support for obsolete imapflags extension for backwards compatibility with CMUSieve.

Added registry for extension capabilities like the available notify methods and adjusted the enotify extension accordingly.

Properly implemented dumping a binary including a list of required extensions and support for extension-specific output.