Upgrade to 0.28 - 9. Custom CSS applied only according scoped restrictions, adapt admin module menu and forms

[entantoencuanto]

[WIP]

This PR:

• Adapts the modals used to create and edit constraints to decidim_modals introduced in 0.28
• Recovers the custom css code applied by scopes defined by admins in awesome menu
• Updates the icons used by the module to use existing declared ones or register new icons specific of the module
• Refactors the secondary nav menu of the module to use the same conventions of Decidim 0.28

Pending: See #257

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

❗ No coverage uploaded for pull request base (redesign@5686e58). Click here to learn what that means.

Additional details and impacted files

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  Hits                ?     3100           
  Misses              ?      253           
  Partials            ?        0           

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