Allow custom reload and stop signals

Hi.

I'm planning to use Daemon::Control to manage an Mojolicious application started with hypnotoad. In hypnotoad there is non-standard [signals](https://metacpan.org/pod/Mojo::Server::Hypnotoad#MANAGER-SIGNALS) that controls the application in an enhanced way, for example doing zero downtime upgrades, and graceful shutdowns (which is the very reason to use hypnotoad in the first place).

It would be nice if the signals used for 'reload' and 'stop' could be mapped to the enhanced ones in hypnotoad. This pull-request adds two attributes ```reload_signal``` and ```stop_signals``` to be able to redefine the signals sent to the application.