Improve "MySQL Threads" graph

[Roman Vynar]

Currently, "MySQL Threads" graph shows:
- Thread Cache Size
- Threads Created

Usually, if thread_cache_size is 0, only threads_created line is shown on the graph. And vice-versa, when thread_cache_size is non-zero (pink area on the graph), usually no new threads are created as the cached ones are used.

Also Threads Cached, Threads Running are not graphed anywhere.

I suggest to amend the existing "MySQL Threads" graph to show the following:
- Thread Cache Size
- Threads Created
- Threads Connected
- Threads Running
- Threads Cached

On the example attached we can observe that once thread_cache_size was set to 10, MySQL stopped creating new threads and started using the cached ones.