Move away from non standard project layout

[athei]

I see no reason why we don't store the contract under src/lib.rs. By storing it under lib.rs we always need to add a Cargo.toml entry. We should stick to the convention and move to src/lib.rs. We then don't add any lib entry to our template. The default will then be to create a rlib crate which is exactly what we want as this is what you need to depend on the crate.

When building the actual contract cargo contract will build the crate as a bin target (as it should).

[SkymanOne]

That should be cargo-contract issue

[ascjones]

I guess we still need to update all the integration-tests here too