Add time frame to quotas

[OpenNebulaProject]

---

Author Name: Carlos Martín (Carlos Martín)
Original Redmine Issue: 3403, https://dev.opennebula.org/issues/3403
Original Date: 2014-12-05

---

Requested during the OpenNebulaConf.

This feature would allow to set an amount of resource-hours for a time frame.
For instance, a user will have 400 cpu-hours for this month. This means he can decide to create small VMs and run them more time, or create bigger one for less time.

OpenNebula needs a way to manage consumable quotas, like a credit system. Ideally these credits can be consumed when a VM is fired or transferred to other users (e.g. group admin to her users)

[rsmontero]

Closing this as duplicate for #1549