[Refactor] Better codebase structure

[wildan3105]

Description

Partially resolves #166

Type of change

• 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 not work as expected)
• Codebase refactoring

Screenshot of change (if there's UI update)

ISSUES

• Favicon is not loaded properly
• Back to home font is a bit weird (black)

ONLY WILL MERGE THIS AFTER THESE PRS ARE ALREADY MERGED:

• Added unit tests for sum and slugify functions in chart.js #175
• Change link color #157 / added 404 link style class #158
• Add watcher gulp for compile scss #159
• [Unit test] feat: add test to spinner utils #169

[wildan3105]

UPDATE
Only first phase, next phase is to remove all github api call to src/api/service.js