contracts: Make ChainExtension trait generic over the runtime

[athei]

This PR changes the ChainExtensions trait to be defined as ChainExtension<C: pallet_contracts::Config>. This is necessary because the ChainExtension::call method has a parameter that is generic over the pallet's configuration. This trait however, only is bound by : frame_system::Config with no way for the ChainExtension implementer to add additional bounds. Therefore calling into any pallet that is not system or contracts would not work because of the missing bounds on that trait.

This PR changes this by giving the implementer the tools to call all runtime functions. A implementation would look like this:

// We assume we are a direct child of the runtime module here
use super::Runtime;

struct TestExtension;

impl ChainExtension<Runtime> for TestExtension {
	fn call<E>(func_id: u32, env: Environment<E, InitState>) -> ExtensionResult<RetVal>
	where
		E: Ext<T = Runtime>,
		<E::T as SysConfig>::AccountId: UncheckedFrom<<E::T as SysConfig>::Hash> + AsRef<[u8]>,
{
        // The `env` is now connected to the runtime and we can call all pallets of the runtime and pass
        //  around types like `E::T::AccountId` that were read from `env.ext()`.
}

@gregzaitsev : This should fix your problem where you weren't able to pass T::AccountId to your pallet.

[athei]

bot merge

[ghost]

Trying merge.