Refactor emoji picker for sub-documents

[virgile-dev]

Feature Request

Is your feature request related to a problem or unsupported use case? Please describe.
Emoji picker for subdocs implementation has been rocky.
At first simple, first caracter of a document or subdoc -> becomes the emoji of the document.
Except, we chose to evolve the behaviour :

• only subdocs can have emojis
• emojis have to be picked from a special selector from side bar or be added through the doc dropdown menu
• emojis do not leave enough space for title when it's long

Describe the solution you'd like
We should revamp this from the ground.
Do we want to go back to simple or add something in the db for it.

Describe alternatives you've considered
A clear and concise description of any alternative solutions or features you've considered.

Discovery, Documentation, Adoption, Migration Strategy
If you can, explain how users will be able to use this and possibly write out some documentation (if applicable).
Maybe add a screenshot or design?

Do you want to work on it through a Pull Request?