Feature/incoming webhooks

[titpetric]

Initial webhooks implementation:

• [x] needs routing configuration with/without jwt middleware,
• [x] needs API sanity check (editing webhooks),
• [x] create a bot user for a webhook message
• [x] manage webhook user avatars

[titpetric]

update:

• add the concept of an outgoing webhook,
• restructure/fix specs and functions on denis's comments

[titpetric]

Important changes introduced:

• tests split into unit / integration and external (documented in wiki),
• permissions have an allow-everything mode for tests via context.WithValue (still requires identity to pass),
• test based entrypoints in individual app/service, needs *testing.T to get full API access
• full integration tests suite, test fixes
• permissions for webhooks as discussed,
• updated static assets packager to goware/statik,
• moved mocks into subfolders (service/mocks/*),
• add commands that trigger outgoing webhooks as the ultimate fallback,
• various style refactoring, constructors, naming, etc.

[codecov-io]

Codecov Report

:exclamation: No coverage uploaded for pull request base (master@9c1b96c). Click here to learn what that means. The diff coverage is 24.09%.

@@            Coverage Diff            @@
##             master     #101   +/-   ##
=========================================
  Coverage          ?   22.79%           
=========================================
  Files             ?      120           
  Lines             ?     7760           
  Branches          ?        0           
=========================================
  Hits              ?     1769           
  Misses            ?     5802           
  Partials          ?      189

Impacted Files	Coverage Δ
crm/rest/request/chart.go	8.47% <ø> (ø)
messaging/internal/repository/util.go	75% <ø> (ø)
crm/rest/request/trigger.go	7.93% <ø> (ø)
crm/rest/request/record.go	8% <ø> (ø)
messaging/internal/repository/repository.go	52.94% <ø> (ø)
system/rest/request/permissions.go	9.09% <ø> (ø)
messaging/types/channel.go	0% <ø> (ø)
system/rest/request/application.go	7.81% <ø> (ø)
messaging/rest/request/search.go	6.45% <ø> (ø)
messaging/internal/repository/attachment.go	41.66% <ø> (ø)
... and 45 more

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[titpetric]

This is a functional webhooks implementation now. Future improvements:

• actually implement avatar storage (should be shared between messaging and system),
• fix webapp* to honor meta fields on systemTypes.User (avatar) and messaging.Message (username, avatar)