feat(frontend): migrate file handler service to Typescript, update frontend test framework and lint

[karrui]

Problem

First PR of many more to migrate angularjs services into plain Typescript services!

This PR migrates the old FileHandler angularjs service to FileHandlerService.

Also fixes jest to be able to run on arbitrary *.test.ts* files.

Solution

Features:

• use new FileHandlerService instead of old client service, remove file-handler.client.service
• update frontend test runner to allow for typescript
• test(FileHandlerService): add unit tests

Tests

Unit tests have been added for FileHandlerService.

• Upload image. Should upload successfully.
• Upload image. Cancel image upload. Should cancel upload (see network and check cancelled) and show cancel error message
• Upload logo. Should upload successfully.
• Upload logo. Cancel logo upload. Should cancel upload (see network and check cancelled) and show cancel error message
• Create form with attachment field. Should behave the same as usual
  • Upload zip with invalid file extensions, should block
  • Upload file with invalid file extension, should block
  • Upload zip with all valid extensions, should succeed
  • Upload file with valid extension, should succeed.

New dependencies:

// spark-md5 is faster and needs less steps to create an md5 hash.
+ "spark-md5": "^3.0.1",
- "crypto-js": "^4.0.0",

New dev dependencies:

// Mock axios in tests
+ "jest-mock-axios": "^4.3.0",

[karrui]

MockAxios seems to have broken axios on the backend even though it's mocked only in public grrrrrrrrrrrrr

[karrui]

uploads do not work (on staging) due to the flawed generation of md5, see https://stackoverflow.com/a/48482000 for more information. WIll fix.

[karrui]

Tested on staging, upload, cancellation, all works! Appreciate a review.