Slowed form opening / white screen

[ponceta]

This is small but the form opening is slightly slowed when we include a document management system widget

You can see the white screen when the form is opened in the capture below.

[domi4484]

Project + data needed to replicate the issue

[3nids]

I think we should implement the same thing than here: opengisch/qgis-ordered-relation-editor#5

[domi4484]

Widgets opening time should be much better in version 0.3.0. Please let me know if it is not the case