Easier add subject/exam buttons in clinical context

[julien-louis]

see #2249

[pierrehenri-dauvergne]

All fine for me but could we also do the same in subject create form:

Center equipment:

Manufacturer:

Coils:

Study cards:

And in the study's details:

Also, maybe it should be another issue, but should we stylise every button the same? Some are dark text and filled with white, others are white text and filled with color:

For example in import:

What do you think ?