adding error checking for hooks & API helper functions

Description

adding error checking for the hooks helper functions and and try/catch clause to API helper to make them less prone to errors or at least easier to understand why something is failing if there is an error with deleting files.

Related Issue

relates to https://github.com/owncloud/web-app-dicom-viewer/issues/48

Motivation and Context

make app less prone to errors and improve debugging

Screenshots (if appropriate):

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)
[x] Tests only (no source changes)

Checklist:

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

owncloud / web-app-dicom-viewer

adding error checking for hooks & API helper functions #54