Update permission system and permission wall to the new system - #289

Fetches the current user's (or non-user's) permissions from the backend instead of using the JWT. The PR compiles without errors when the backend changes are used. Changes:

• Use the new (improved!) getMyPermissions router from the backend instead of the unconventional JWT permission hack
• New method for accessing permissions (usePermissions)
• Adding loading skeleton to admin sidebar
• Clear queryClient cache when logging out and in
• Tiny unrelated and inconsequential bugfixes

Since the PR changes how Permission wall picks up permissions, it needs to be pushed to prod right after the corresponding backend fixes:

• Removed reliance on pelicanq fork of fastapi-users WebWebWeb#525