Use a more sophisticated template for end-to-end testing.

Created by: EnoahNetzach

This continues #875 and fixes #706 (closed).

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Tested features

es6 syntax

• JSX
• Flow
• Promises
• arrow functions
• generators
• async/await
• class properties
• property shorthand
• computed properties
• template string interpolation
• custom string interpolation
• param default
• destructuring
• spread operator
• rest parameters
• rest + default (@see https://github.com/babel/babel/issues/4851)
• destructuring + await (@see #1160 (closed))

env variables

• NODE_PATH
• custom env variables via shell
• .env file

webpack plugins

• svg inclusion
• image inclusion
• json inclusion
• css inclusion
• no-ext inclusion
• unknown-ext inclusion

Test suites

• test env
• development env
• production env
• flow integration (@see #1152)