* Receiver, aggregate, server finished.

@lemon @ascrutae I change the proto file path for preparing 6.0, but didn't change .net namespace. But I think if you sync the protocol submodule, you still need some changes.

Fix #1435

* #1447

Fixed the after method interceptor for the apache http client NPE error when the response is null cause by the doExecute method throw a exception.

Make the icon font things more clear in NOTICE, include where they are in our source folder. Also move the text at the beginning of the distribution NOTICE file. (#1444)

* Cluster module implementation finished.

* Fix #1441 add icon files notice

* Amend notice file, add excluding icon folder in rat config

Sync English documents to Chinese.

* Add Junit test for ribbon's NIWSServerListClassName

* Add License Head to Code file

* try to solve submodule skywalking-ui conflict

# Conflicts:
#	README_ZH.md

Init branch 6.0 for our next big iteration. Change root readme. Format field document in table.  Remove Chinese documents.

Fixed the bug of the result of GC count in query of GC trend service always 0.

* Update How-to-release.md

* Update create_source_release.sh

* Update README.md

* Update README_ZH.md

Error rate alarm is not triggered