Image Embedding - show more descriptive error

[PrimozGodec]

Issue

The error that the Image Embedding widget shows do not describe what happened. It just shows the type of error (for example OSError).

Description of changes

Show the error text instead of the error type

Includes

• [X] Code changes
• [X] Tests
• [ ] Documentation

[codecov[bot]]

Codecov Report

Merging #224 (a4b510f) into master (8f8e759) will decrease coverage by 0.03%. The diff coverage is 100.00%.

Additional details and impacted files

```diff @@ Coverage Diff @@ ## master #224 +/- ## ========================================== - Coverage 69.07% 69.05% -0.03% ========================================== Files 17 17 Lines 2826 2824 -2 Branches 392 392 ========================================== - Hits 1952 1950 -2 Misses 765 765 Partials 109 109 ```