Add OpenAPI to get application information

[kezhenxu94]

This patch exposes a new Open API (/apps) to allow third-party client to get application information, as stated in issue #1648

[codecov-io]

Codecov Report

Merging #2072 into master will decrease coverage by 0.27%.
The diff coverage is 6.89%.

@@             Coverage Diff              @@
##             master    #2072      +/-   ##
============================================
- Coverage     50.25%   49.97%   -0.28%     
+ Complexity     1981     1979       -2     
============================================
  Files           400      401       +1     
  Lines         12349    12406      +57     
  Branches       1275     1278       +3     
============================================
- Hits           6206     6200       -6     
- Misses         5686     5748      +62     
- Partials        457      458       +1

Impacted Files	Coverage Δ	Complexity Δ
...ork/apollo/openapi/client/ApolloOpenApiClient.java	50.94% <0%> (-2%)	4 <0> (ø)
...ctrip/framework/apollo/openapi/dto/OpenAppDTO.java	0% <0%> (ø)	0 <0> (?)
...ramework/apollo/openapi/util/OpenApiBeanUtils.java	0% <0%> (ø)	0 <0> (ø)	⬇️
...ollo/openapi/client/service/AppOpenApiService.java	55% <20%> (-35%)	3 <0> (ø)
...rk/apollo/openapi/v1/controller/AppController.java	25% <28.57%> (-3.58%)	1 <1> (ø)
...work/apollo/biz/message/DatabaseMessageSender.java	57.14% <0%> (-10.21%)	6% <0%> (-2%)
...mework/apollo/portal/component/PortalSettings.java	65.07% <0%> (-4.77%)	5% <0%> (ø)
.../apollo/internals/RemoteConfigLongPollService.java	79.14% <0%> (-1.23%)	27% <0%> (-1%)
...ework/apollo/internals/RemoteConfigRepository.java	87.89% <0%> (+0.63%)	23% <0%> (+1%)	⬆️

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[coveralls]

Coverage decreased (-0.3%) to 53.668% when pulling 1361ed2 on kezhenxu94:feature/openapi-get-apps-info into 21e76b3 on ctripcorp:master.