1. Moved Volume to separate file
  2. Created IVolume interface and implemented current behaviour in implementation of new interface — VolumeJBOD
  3. Replaced all old volume usages with new VolumeJBOD. Where it is unnecessary to have JBOD — left just IVolume.
  4. Removed old Volume completely
  5. Moved StoragePolicy to separated files
  6. Moved DiskSelector to separated files
  7. Removed DiskSpaceMonitor file

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

correct fallback for PREFER_PARTIAL_MERGE: HashJoin -> MergeJoin instead of HashJoin -> JoinSwitcher

This patch adds <tmp_policy> config directive, that will define the
policy to use for storing temporary files, if it is not set (default)
the <tmp_path> will be used.

Also tmp_policy has some limitations:
- move_factor              is ignored
- keep_free_space_bytes    is ignored
- max_data_part_size_bytes is ignored
- must have exactly one volume

Rename SettingsCommon.h -> SettingsCollection.h for consistency.