CPU and RAM usage

### Description
> Right now the stats show the contribution of each user or nickname group but offers no insight about CPU and RAM usage. This is very unhandy as different tasks have different workloads, which are stats that are important to developers
### Solution
> The CPU and RAM usage should be logged at all times in order to be able to compute some interesting statistics for the requester.
> This data can then be used to compute three graphs (CPU and RAM):
> - The local resource usage graph (uses data from the same computer code is running on)
> - The internal resource usage graph (uses data from the same user/nickname group) → requires #67
> - The external/global resource usage graph (uses data from all users helping/who helped the task)