[Plato imports] Proxies & Plato improvements

[mietcls]

Draft, to be prioritised and refined

Algemene Plato epic: #1348

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Bugs

Encoding issues [secondary]
#1642

Supervisor draft en withdrawn: zichtbaar in dashboard [not a bug but a decision]
#1715

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PR review nodig:

Removed suggestion
#1728

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Later:

• Add search to proxy dashboard (later, now ctrl + f)

Miet only

• fix title in header (more similar to overview?)
• bib message read-only on different tabs
• Hide biblio-rejected for researchers
• Small improvements: copy and layout #1679

Plato:

• Hide rejected suggestions for researchers when removed by librarian

Forms:

• make 4 questions required

[mietcls]

Restructured in other issues