Improved self-hosted server.

- Will now stop the self-hosted server _and exit_ the program on INT and TERM signals.
- No more multiple Sinatra messages on multiple signals.
- Stopping/quitting a server possible using .quit! and without the need of the actual server and handler_name.
Simplify and Improve readability on some conditions
Merge pull request #1 from scudelletti/self-hosted_server

Simplify and Improve readability on some conditions
Further refactored the self-hosted server behaviour.
Merge pull request #710 from tbuehlmann/self-hosted_server

Improved self-hosted server.