add cassandra support

[LeoQuote]

1. 重构 engine 部分, 前端自动发现已启用的 engine
2. 新增 cassandra 支持
3. data dictionary 部分防攻击

[request-info]

你好!感谢你反馈的问题/bug，但是你的描述好像是空的，我们需要你完整的信息，这样才能帮你解决问题 如果不知道怎么写，在新建issue的时候有若干个模板可供选择，祝好！

[codecov]

Codecov Report

Patch coverage: 87.50% and project coverage change: +0.38% 🎉

Comparison is base (6018ae8) 75.14% compared to head (620ff4a) 75.53%.

Additional details and impacted files

@@            Coverage Diff             @@
##           master    #2230      +/-   ##
==========================================
+ Coverage   75.14%   75.53%   +0.38%     
==========================================
  Files         105      107       +2     
  Lines       15196    15454     +258     
==========================================
+ Hits        11419    11673     +254     
- Misses       3777     3781       +4     

Files Changed	Coverage Δ
sql/instance.py	51.58% <0.00%> (ø)
sql/models.py	96.58% <ø> (ø)
sql/engines/mongo.py	60.99% <50.00%> (-0.08%)	⬇️
sql/engines/cassandra.py	84.45% <84.45%> (ø)
sql/engines/test_cassandra.py	90.29% <90.29%> (ø)
sql/data_dictionary.py	98.96% <93.75%> (-1.04%)	⬇️
sql/engines/__init__.py	70.17% <93.75%> (+3.82%)	⬆️
archery/settings.py	58.55% <100.00%> (+1.28%)	⬆️
sql/engines/clickhouse.py	71.60% <100.00%> (-0.46%)	⬇️
sql/engines/goinception.py	66.03% <100.00%> (+0.29%)	⬆️
... and 9 more

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[nick2wang]

完美，readme也麻烦更新一下支持清单吧，辛苦了👏