[Event Request] Disk IO

A requestable event showing I/O activity for a disk.
Defaults to every 20 seconds.

*Event Name:* Disk IO
|| Attribute name || Description || Content type || Type || \[Value range\] or Example Value || Relational Key |
| Device | unique interface identifier | | String | "sda" | (/) |
| Read utilization | a fraction of the full utilization | percentage | float | \[0,1\] | (x) |
| Write utilization | a fraction of the full utilization | percentage | float | \[0,1\] | (x) |
| Read rate | read rate in bytes per second | unknown | long | 1334134 | (x) |
| Write rate | write rate in bytes per second | unknown | long | 1324534 | (x) |

_*Note:* This is essentially the same event as Network IO, and you could very well imagine just having one event type - "Device IO", and introduce a type parameter. This may make actually make more sense to Mission Control as well, as you can easily add more events to the JVM without changing the GUI. Something to consider. Also, again, rate is probably easier to implement than utilization._