feat(dapp-lib): integrated multi-signature server

[LeonLi000]

1. multi-signature server features: simple and easy to use, can be deployed independently.
2. provide two signature interfaces based on json rpc.
3. some modifications have been made to the off-chain adaptation of the multi-signature server.

[codecov-io]

Codecov Report

Merging #219 (5b0e463) into dapp-lib (a20f402) will not change coverage. The diff coverage is n/a.

:exclamation: Current head 5b0e463 differs from pull request most recent head 882254c. Consider uploading reports for the commit 882254c to get more accurate results

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##           dapp-lib     #219   +/-   ##
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  Coverage     36.43%   36.43%           
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  Files            47       47           
  Lines          5778     5778           
  Branches         83       83           
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  Hits           2105     2105           
  Misses         3673     3673           

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[e00dan]

Hi there, can I ask what's the status of this pull request?