Hide Time Tracking estimates from certain users (e.g. customers)

Today everybody can see time estimates made on an issue. It would be nice if it was possible (for example via the permission scheme) to determine who should be able see them.

An idea to the level of permissions could be:

• Edit others time estimates
• Add/Edit own time estimates
• View time estimates

1. The agency wants to be able to control who can see any time estimation and tracking information, such as customers (likely not), internal project management (rather yes) etc.
2. In some circumstances, this information is sensitive and needs to be handled accordingly.