TestSessionEnvironment by default will create a temporary database for
use with behat tests, but this may not be required.
e.g. in your behat.yml:
```
default:
...
extensions:
...
SilverStripe\BehatExtension\Extension:
create_temp_database: false
```
Removed framework_host since its no longer necessary due to the changed execution logic.
Unfortunately had to subclass the existing Mink Extension class since we can't influence
its config persistence from our own extensions (with a completely separate ContainerBuilder).
Also restructured README to be more focused on execution rather
than diving into deep config concerns early on.
- Moved all extension-specific conf into its own configuration namespace
- Described configuration via PHP, and added default values
- Removed boilerplate config from README
- Made screenshot_path optional
- Configurable ajax_timeout settings
Note: The DI system plus the initializer+context combo requires insane amounts of code duplication,
will need to be looked at more closely (very little docs on that level of Behat extension available).
