refact(rpc): merge rpc module into commons

[imbajin]

for apache need, after this pr, we will:

• [x] rename hugegraph-common --> hugegraph-commons
• [x] merge the hugegraph-rpc module into hugegraph-commons, and keep it independent (include commit log)
• [x] merge License, checkstyle, ci, etc..
• [x] add a new pom.xml & README in root dir
• [ ] unify rpc & common version later (better to keep same)

[codecov[bot]]

Codecov Report

Merging #84 (6e2330d) into master (1d27452) will increase coverage by 4.09%. The diff coverage is 93.12%.

:exclamation: Current head 6e2330d differs from pull request most recent head ee08712. Consider uploading reports for the commit ee08712 to get more accurate results

@@             Coverage Diff              @@
##             master      #84      +/-   ##
============================================
+ Coverage     89.03%   93.12%   +4.09%     
+ Complexity      943       65     -878     
============================================
  Files            63        9      -54     
  Lines          2744      262    -2482     
  Branches        399       22     -377     
============================================
- Hits           2443      244    -2199     
+ Misses          154        8     -146     
+ Partials        147       10     -137     

Impacted Files	Coverage Δ
...n/java/com/baidu/hugegraph/version/RpcVersion.java	50.00% <50.00%> (ø)
...ava/com/baidu/hugegraph/rpc/RpcClientProvider.java	90.47% <90.47%> (ø)
...ava/com/baidu/hugegraph/rpc/RpcConsumerConfig.java	91.48% <91.48%> (ø)
.../java/com/baidu/hugegraph/rpc/RpcCommonConfig.java	91.66% <91.66%> (ø)
...c/main/java/com/baidu/hugegraph/rpc/RpcServer.java	92.06% <92.06%> (ø)
...in/java/com/baidu/hugegraph/config/RpcOptions.java	97.22% <97.22%> (ø)
...ain/java/com/baidu/hugegraph/rpc/RpcException.java	100.00% <100.00%> (ø)
...ava/com/baidu/hugegraph/rpc/RpcProviderConfig.java	100.00% <100.00%> (ø)
...m/baidu/hugegraph/rpc/RpcServiceConfig4Client.java	100.00% <100.00%> (ø)
...ava/com/baidu/hugegraph/concurrent/AtomicLock.java
... and 62 more

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[imbajin]

after review & CI pass, separate this pr into 2