Add referencing steps as components

[kwalter94]

1. A new field named components is introduced
2. The components field takes a list of namespaces
3. Each namespace takes a list of components
4. Steps can reference components through a componentId

A sample configuration below:

url: http://localhost:7654
dial: "*1234*1234#"
phoneNumber: 265888123456
sessions:
  - id: check-balance
    phoneNumber: 265888123456
    description: "Should return a balance of 500 for Zikani"
    steps:
      # Component IDs can be namespaced (e.g. default.login),
      # "default" namespace can be omitted as below
      - componentId: "login"
      - userInput: "Zikani"
        componentId: "default.home"
      - userInput: "2"
        componentId: "check-balance.display-balance"
  - id: update-account-name:
    steps:
        - componentId: "login"
        - userInput: "Zikani"
          componentId: "home"
        - userInput: "2"
          componentId: "account-detail.home"
        - userInput: 1
          expect: Enter your new name:
  - id: request-account-statement:
    steps:
        - componentId: "login"
        - userInput: "Zikani"
          componentId: "home"
        - userInput: "2"
          componentId: "account-detail.home"
        - userInput: 2
          expect: "Your statement is being processed!"
components:
  - namespace: default
    items:
      - id: login
        expect: "What is your name?"
      - id: home
        expect: |-
          Welcome, Zikani
          Choose an item:
          1. Account detail
          2. Balance
          3. Something else
          # Exit
  - namespace: check-balance
    items:
      - id: display-balance
        expect: "You are broke!"
  - namespace: account-detail
    items:
      - id: home
        expect: |-
          1. Change name
          2. Statement

Partially addresses #8

[zikani03]

@kwalter94 this is looking great, awesome work!