Remove yarn and upgrade to vue-cli 3

[zhouzhuojie]

Description

• Remove yarn and use npm instead
• Move to vue-cli v3
  • Refactor how we set env
  • Refactor VUE_APP_FLAGR_UI_POSSIBLE_ENTITY_TYPES in the UI. We still keep the same Dockerfile build-args FLAGR_UI_POSSIBLE_ENTITY_TYPES
• Bump axios
• Refactor how to build the Dockfile
  • Remove Dockerfile-CI and in favor of official docker images (golang:1.12 and node:10)
  • Refactor circleci tests

Motivation and Context

• To keep up the current vue-cli version
• To leverage official docker image instead of flagr-ci image
• Migrate from yarn to npm

How Has This Been Tested?

Tested locally. Also tested with FLAGR_WEB_PREFIX.

Types of changes

• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to change)

Checklist:

• My code follows the code style of this project.
• My change requires a change to the documentation.
• I have updated the documentation accordingly.
• I have added tests to cover my changes.
• All new and existing tests passed.

[codecov-io]

Codecov Report

Merging #265 into master will not change coverage.
The diff coverage is n/a.

@@           Coverage Diff           @@
##           master     #265   +/-   ##
=======================================
  Coverage   81.76%   81.76%           
=======================================
  Files          26       26           
  Lines        1530     1530           
=======================================
  Hits         1251     1251           
  Misses        210      210           
  Partials       69       69

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