🔥Docker and environment variables cleanup (#270)

* Added dotenv-rails gem to manage environment variables

* Added dotenv-rails gem to manage environment variables
* Removed figaro which was used earlier for this purpose

* Standardized variable names

* Changed all env variables to be upper case. This included changes in files referencing env variables.
* Added example env file with all variables set to empty value
* Removed the earlier setup of copying application.yml and database.yml and the scripts and documentation associated to this

* Docker setup

* Added docker file for building the docker images
* Added entrypoint.sh script which is referenced inside the Docker image
* Cloned the Procfile for development using docker which has slight change compared to regular procfile
* Added the docker-compose.yml which has 3 service's configuration, postgres, redis and chatwoot server and a mounted volume for postgres

* Added docker related info to documentation

* Added the docker setup info in the documentation
* Added info for using`rbenv` instead of rvm for managing ruby versions
* Updated the documentation for environment variables to have one about `dotenv-rails` gem and removed the documentation about the old copy paste method used by figaro

* Changing the postgres database, username and password as environment variables

* Removed database.yml from gitignore
* Made the postgres databse, username and password as environemnt variables
* Added this in documentation

* Added a quick setup page

* Added quick setup page
* Removed the docs from README and added link to the docs in website
* Removed the figaro related things from circle.ci config

* Adding external volume for redis in docker compose

* Added instructions for adding the redis volume in docs

docker-compose.yaml

@@ -0,0 +1,44 @@
+version: '3'
+services:
+
+  server: &server
+    build:
+      context: .
+      dockerfile: ./docker/Dockerfile
+    volumes:
+      - ./:/app
+    links:
+      - postgres
+      - redis
+    ports:
+      - '3000:3000'
+    environment:
+      - REDIS_URL=redis://redis:6379
+      - POSTGRES_HOST=postgres
+    command: ["foreman", "start", "-f", "./docker/Procfile.docker.dev"]
+
+  postgres:
+    image: postgres:9.6
+    restart: always
+    ports:
+      - '5432:5432'
+    volumes:
+      - postgres:/data/postgres
+    environment:
+      - POSTGRES_DB=chatwoot
+      - POSTGRES_USER=postgres
+      - POSTGRES_PASSWORD=
+
+  redis:
+    image: redis:alpine
+    restart: always
+    volumes:
+      - redis:/data/redis
+    ports:
+      - '6379:6379'
+
+volumes:
+  postgres:
+    external: true
+  redis:
+    external: true