[#20] Initial version of RIC API Gateway

[woojoong88]

This is the initial version of RIC API Gateway (v0.1.0). This gateway is running in between RIC Southbound and all other applications (e.g., Redis DB, ONOS, XOS, and all other applications). Like switch, this gateway receives API messages and transmits the messages. Here is the feature in the first version.

• This gateway is now running on Apache Celix framework which is one of OSGi frameworks. Due to this framework, we can dynamically stop, start, update, install, and uninstall all bundles. For example, we need to connect a new third party application with the gateway. Without Celix framework, we should shutdown this gateway, build a new code, and run this gateway again. This leads to a service disruption time which will be critical. With Celix framework, we don't need to shutdown everything. Just we build a new code to communicate with the new third party application and install in on Celix framework with CLI.
• It only has CellConfigReport processing logic.
• In this gateway, there are three gateway bundles, (i) Gateway core bundle (GWCore), (ii) Southbound bundle (SBBundle), and (iii) RedisBundle. GWCore is the core bundle to run this gateway, which controls all bundles.
• It supports remote access through telnet (telnet port 6666).

Future work

• Expand more processing logic for each control message from Southbound.
• Implement match-action table on GWCore so that we can multiplex a single control message from any application to the other applications according to rules.
• Develop Sample bundles for other guys.
• Develop XOS and ONOS bundles to communicate with XOS and ONOS, respectively.
• Develop a bundle to set match-action rules through REST or gRPC.

[woojoong88]

I realized that there is a memory leaking problem in RedisBundle. I fixed it at the last commit.