Cover Vetur's Language Features with ene-to-end tests

[octref]

https://github.com/octref/vscode-language-server-e2e-test

• Infrastructure from https://github.com/octref/vscode-language-server-e2e-test
• Basic formatting
• Basic definition
• Full formatting
• Full definition
• Completion
  • Template
  • Style
  • Script
• Diagnostics
• Hover
• Highlight
• References
• Document Link
• Document Symbol
• Color Presentation — later, will need to update LanguageServer node module first
• Signature Help — later, this is only available to <script> section and that is tightly coupled with the TS version we are using (about to update).

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• Setup travis so e2e test runs together with unit tests
• Setup coverage report — seems too tricky with mocha + TypeScript and then our extension setup

Functionalities:

• Reenable documentLink

[octref]

@HerringtonDarkholme FYI, think these tests are much easier to write.

@ktsn I'll update the type-checking PR with E2E tests. Otherwise it's impossible to mock up everything for testing.

[HerringtonDarkholme]

Sounds Great! E2E test is better for script/style integration than unit test. Thanks for bringing about e2e framework!