Currently the size of our distribute package is up to
800MB, this patch is migrate python gateway server into
api server
The distribute package size before and after this patch is:
```sh
# before
796M apache-dolphinscheduler-2.0.4-SNAPSHOT-bin.tar.gz
# after
647M apache-dolphinscheduler-2.0.4-SNAPSHOT-bin.tar.gz
```
* Add basic cli mechanism with Click, for now just including
one single subcommand `version`
* Add general and easy test class in tests/testing/cli, and
test to version
* Add sphinx-click to general cli docs basic on click
Jiajie Zhong