Change quotas at runtime

- a user can update the default quota if she/he has the permission to do so (e.g. `quotas/write`)
- an API call will allow updating the project quota (e.g. `PUT /v1/quotas/{org}/{proj}`)
- Fusion will allow editing the quota configuration if the user has the quota specific permission on the viewed project
- Lowering the quota should have no effect on existing resources
- a quota value can be set lower than the current number of resources, files, size; no check will be performed to validate the quota value with respect to the resources in the project
- a quota value cannot be negative
- a quota value of 0 does not allow the creation of new resources
- a quota value of 0 does not block the creation of the default project resources

Start by tracing the existing quota configuration and permission handling for the `PUT /v1/quotas/{org}/{proj}` API and the Fusion quota editor. Confirm how project resources and default resources are created before implementing the listed runtime-update, non-negative, and zero-quota rules; done means all stated behaviors are enforced.

Written by the indexing model from the issue text.