Added support for acknowledgement from other nodes in open/close index api

The open/close index api now waits for an acknowledgement from all the other nodes before returning its response, till the timeout (configurable, default 10 secs) expires. The returned acknowledged flag reflects whether the cluster state change was acknowledged by all the nodes or the timeout expired before.

Closes #3400
Updated test to reflect added acknowledgement from all nodes in open/close index api

If it's acknowledged all the other nodes already hold the latest cluster state, thus we can search on the closed index and be sure we get an error back
Renamed MetaDataStateIndexService to MetaDataIndexStateService for consistency
completed renaming of MetaDataStateIndexService to MetaDataIndexStateService
Added version support to mget and get apis, that only will perform the get operation if the version of the document to be fetched matches with the provided version.

Both get and mget apis now support the following additional parameters: `version` and `version_type`.

Closes #3404
Rewrote the percolate existing doc api.
The percolate existing doc feature now reuses the get request instead of having a separate request body.
Relates to #3380
Moved node level classes classes out of the index.percolator package into toplevel percolator package.
Added source fetching and filtering parameters to search, get, multi-get, get-source and explain requests

Closes #3301