Add support of dockerimage tool in Devfile

[sleshchenko]

Description

Add support of dockerimage tool in Devfile.
dockerimage tool format should allow to specify dockerimage like (eclipse/che-server:nightly) and Che specific fields for defining volumes, servers, env vars, etc. See the following example of possible format

---
version: 0.0.1
name: petclinic-dev-environment
projects:
  - name: petclinic
    source:
      type: git
      location: 'git@github.com:spring-projects/spring-petclinic.git'
tools:
  - name: maven
    type: dockerimage
    image: maven:3.5.4-jdk-8
    volumes:
      - name: maven-repo
        containerPath: /root/.m2
    env:
      - name: ENV_VAR
        value: value
    endpoints:
      - name: maven-server
        port: 3101
        attributes: 
          protocol: http
          secure: true
          public: true
          discoverable: false
    memoryLimit: 1500M
    mountSources: true
  - name: theia-ide
    type: cheEditor
    id: eclipse/theia:0.0.3
  - name: maven-sidecar
    type: chePlugin
    id: eclipse/maven-sidecar:0.0.3
commands:
  - name: build
    actions:
      - type: exec
        tool: maven
        command: mvn package
        workdir: /projects/spring-petclinic

The format should be sync with che-plugin.yaml format. See Plugin Java Model, che-plugin.yaml example

[sleshchenko]

@garagatyi @l0rd @skabashnyuk Are you OK with proposed model (see issue description) for dockerimage tool?

[garagatyi]

Looks good to me

[l0rd]

LGTM too

[sleshchenko]

Added memoryLimit field to dockerimage tool model

[sleshchenko]

Added mountSources field to dockerimage tool model

[skabashnyuk]

LGTM