Rewrite IMAP-Module to buffer its output

Rewrite IMAP-Module to buffer its output

 - move defines from imap_tools.h into serv_imap.h
 - switch includes in sequence
 - we now have IMAP->Reply, which we write into, until IUnbuffer sends it to the client
 - IReply & IReplyPrintf do now send 'Params[0].Key BAD xxxxxx\r\n' to the client; this makes the code more compact.
 - IA* append stuff to the outbuffer that we want to send.
 - replace rumpelstilskin handler lookup by hashlist and central register calls.
 - replace if's in the sequence separating the handlers by their required pre-conditions by flags on the register call.

this should
 - (hopefully) fix some troubles with evolutions imap, which wouldn't like to read enough chunks until the line ends
 - speed up stuff like header fetching in huge lists, since we reduce the number of context switches here.