Tidied some things up after initial setup.

While installing the project locally, I encountered some minor issues. I "fixed" (or adjusted) the following:

* Added and changed some lines to `.gitignore`.
* Added some `.gitkeep` files to preserve directories.
* Removed files in `/bin` (those are installed by composer).
* Added support for `unix_socket` setting for Doctrine.
* Changed `delivery_address` setting to `mailer_delivery_address` and moved it to the other mailer stuff.

And while at it, I updated the README.