refactor(delivery): redesign && rewrite

[mydearxym]

重新设计并重写了整个内部消息系统，原先的设计不合理且过于复杂。

[codecov]

Codecov Report

Merging #404 (1bf1976) into dev (380330d) will decrease coverage by 0.67%.
The diff coverage is 100.00%.

@@            Coverage Diff             @@
##              dev     #404      +/-   ##
==========================================
- Coverage   87.60%   86.93%   -0.68%     
==========================================
  Files          63       59       -4     
  Lines        1138     1079      -59     
==========================================
- Hits          997      938      -59     
  Misses        141      141              

Impacted Files	Coverage Δ
lib/groupher_server/accounts/accounts.ex	90.47% <ø> (ø)
lib/groupher_server/cms/cms.ex	97.56% <ø> (ø)
...groupher_server_web/resolvers/accounts_resolver.ex	90.32% <ø> (ø)
lib/groupher_server_web/schema.ex	100.00% <ø> (ø)
test/support/assert_helper.ex	96.55% <ø> (ø)
test/support/factory.ex	86.45% <ø> (ø)
lib/groupher_server/accounts/delegates/fans.ex	100.00% <100.00%> (ø)
lib/groupher_server/accounts/delegates/profile.ex	86.36% <100.00%> (ø)
lib/groupher_server/cms/delegates/article_curd.ex	100.00% <100.00%> (ø)
lib/groupher_server/cms/delegates/comment_curd.ex	100.00% <100.00%> (ø)
... and 14 more

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