Feature: Slack integration (#783)

- Integrations architecture
- Slack integration

Gemfile.lock

@@ -143,6 +143,8 @@ GEM
       descendants_tracker (~> 0.0.1)
     concurrent-ruby (1.1.6)
     connection_pool (2.2.2)
+    crack (0.4.3)
+      safe_yaml (~> 1.0.0)
     crass (1.0.6)
     datetime_picker_rails (0.0.7)
       momentjs-rails (>= 2.8.1)
@@ -191,6 +193,7 @@ GEM
     ffi (1.12.2)
     flag_shih_tzu (0.3.23)
     foreman (0.87.1)
+    gli (2.19.0)
     globalid (0.4.2)
       activesupport (>= 4.2.0)
     google-api-client (0.39.4)
@@ -225,6 +228,7 @@ GEM
       activesupport (>= 5)
     haikunator (1.1.0)
     hana (1.3.6)
+    hashdiff (1.0.1)
     hashie (4.1.0)
     hkdf (0.3.0)
     http-accept (1.7.0)
@@ -411,6 +415,7 @@ GEM
     rubocop-rspec (1.39.0)
       rubocop (>= 0.68.1)
     ruby-progressbar (1.10.1)
+    safe_yaml (1.0.5)
     sass (3.7.4)
       sass-listen (~> 4.0.0)
     sass-listen (4.0.0)
@@ -452,6 +457,13 @@ GEM
       json (>= 1.8, < 3)
       simplecov-html (~> 0.10.0)
     simplecov-html (0.10.2)
+    slack-ruby-client (0.14.6)
+      activesupport
+      faraday (>= 0.9)
+      faraday_middleware
+      gli
+      hashie
+      websocket-driver
     spring (2.1.0)
     spring-watcher-listen (2.0.1)
       listen (>= 2.7, < 4.0)
@@ -507,6 +519,10 @@ GEM
       activemodel (>= 6.0.0)
       bindex (>= 0.4.0)
       railties (>= 6.0.0)
+    webmock (3.8.3)
+      addressable (>= 2.3.6)
+      crack (>= 0.3.2)
+      hashdiff (>= 0.4.0, < 2.0.0)
     webpacker (5.1.1)
       activesupport (>= 5.2)
       rack-proxy (>= 0.6.1)
@@ -583,6 +599,7 @@ DEPENDENCIES
   shoulda-matchers
   sidekiq
   simplecov (= 0.17.1)
+  slack-ruby-client
   spring
   spring-watcher-listen
   telegram-bot-ruby
@@ -594,6 +611,7 @@ DEPENDENCIES
   uglifier
   valid_email2
   web-console
+  webmock
   webpacker
   webpush
   wisper (= 2.0.0)