* Refactoring: part 1

* Refactoring: part 2

* Handle request using ReadBuffer interface

* Struggles with ReadBuffer's

* Fix URI parsing

* Implement parsing of multipart/form-data

* Check HTTP_LENGTH_REQUIRED before eof() or will hang

* Fix HTTPChunkedReadBuffer

* Fix build and style

* Fix test

* Resist double-eof

* Fix arcadian build

We are breaking backwards compatibility anyway (but agted by a setting)

For now uuids are not generated at all, they are present only if the
part is updated manually (as you can see in the integration test).

The only place where they can be seen today by an end user is in
`system.parts` table. I was looking for hiding this column behind an
option but couldn't find an easy way to do that.

Likely this is also required for WAL, but need to think how not to break
compatibility.

Relates to #13574, https://github.com/ClickHouse/ClickHouse/issues/13574

Next 1: In the upcoming PR the plan is to integrate de-duplication based on
these fingerprints in the query pipeline.

Next 2: We'll enable automatic generation of uuids and come up with a
way for conditionally sending uuids when processing distributed queries
only when part movement is in progress.

* Move some code outside dbms/src folder
* Fix paths

Also a couple of massive include-refactorings with better forwarding

DataPartsExchange new protocol with data size. StorageReplicatedMergeTree::fetchPartition multipath fix. Choosing on mutate any disk to write mutation file.

This reverts commit cdb2c8a7.

This reverts commit 0704da57, reversing
changes made to 4534d449.

* Add ATTACH PARTITION FROM table for MergeTree. [#CLICKHOUSE-3546]

* Implemented replicated case on non-leader replica. [#CLICKHOUSE-3546]

* Disable merges in the dropping range. [#CLICKHOUSE-3546]

* DROP PARTITION is atomic and simpler now. [#CLICKHOUSE-3546]

* Implemented more SYSTEM queries. [#CLICKHOUSE-2931] [#CLICKHOUSE-3546]

SYSTEM queries:
RESTART REPLICAS
SYNC REPLICA db.name
STOP MERGES [db.name]
START MERGES [db.name]
STOP FETCHES [db.name]
START FETCHES [db.name]
STOP REPLICATED SENDS [db.name]
START REPLICATED SENDS [db.name]
STOP REPLICATION QUEUES [db.name]
START REPLICATION QUEUES [db.name]

* Fixed a bunch of bugs in REPLACE PARTITION. [#CLICKHOUSE-3546]

* Add tests for REPLACE PARTITION and SYSTEM. [#CLICKHOUSE-3546]

* Add system.part_log logging. [#CLICKHOUSE-3546]

* Fixed long wait in SYNC REPLICA. [#CLICKHOUSE-3546]

* Add requested changes. [#CLICKHOUSE-3546]

Fixed clickhouse-client bad return code.

* Add requested chenges. [#CLICKHOUSE-3546]

* Add requested chenges. [#CLICKHOUSE-3546]

* ReplicatedMergeTree: Max streams to send data [#CLICKHOUSE-2878]

* fix

* better messages on client

* change code to 429 TOO_MANY_REQUESTS

* wip

* better message

* Update InterserverIOHandler.h

* Update InterserverIOHTTPHandler.cpp

* Update StorageReplicatedMergeTree.cpp

This reverts commit abaa1501.