Add possibility of remove pings/events cascade deleting on check remove

If we have checks with huge pings/events history, the cascade delete is very long and painful. :snail:

I added here the possibility of desactivate the cascade deletion in config file.
If you desactivate it pings or/and events won't be removed on check delete. In any case, it will be remove because of `pingHistory` configuration for analyzer.

The two parameters are set to `true` by default in order to avoid BC break.

You **MUST** merge PR #246 before this! If not, the app will crash like described in #243 or #218.

I'm not an expert of NodeJS, so don't hesitate to give me some reviews! ;)