Refactoring metadatahandling

Description

Refactoring where Metadata is extracted and how it is handled in the app (data format/storage). Added extractMetadata helper class and tags look up table, adjusted test cases that included metadata props.

Related Issue

Fixes issues with extensive mocking and testability

Motivation and Context

previously the App.vue file had about 1000 lines of code and it was difficult to test. Separating the cornerstone core features from our own functionalities for extracting and handling metadata makes it easier to test (previously each test case required extensive mocking of cornerstone functions). The new solution is more modular and thus easier to scale/further extend and test.

Screenshots (if appropriate):

Types of changes

[x] 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)
[ ] Tests only (no source changes)

Checklist:

[x] Code changes
[x] Unit tests added/modified
[ ] Acceptance tests added

owncloud / web-app-dicom-viewer