Clean up module imports in Cargo

[MrDarthShoe]

Currently in relay-client there are following dependencies in cargo.toml:

[dependencies]
ya-relay-stack = "0.5.0"
ya-relay-proto = "0.4.2"
ya-relay-core = "0.4.0"

And workspace cargo.toml has following patches:

[patch.crates-io]
ya-relay-client = { path = "client" }
ya-relay-core = { path = "crates/core" }
ya-relay-proto = { path = "crates/proto" }
ya-relay-stack = { path = "crates/stack" }
ya-relay-util = { path = "crates/util" }
ya-relay-server = { path = "server" }

By doing it, when somebody uses ya-relay-client revision instead of released one, he needs to patch these manually like so:

[patch.crates-io]
ya-relay-stack = { git = "https://github.com/golemfactory/ya-relay.git", rev = "506a678ef65893e9c0d857e4d7b8f84999790928" }
ya-relay-client = { git = "https://github.com/golemfactory/ya-relay.git", rev = "506a678ef65893e9c0d857e4d7b8f84999790928" }
ya-relay-core = { git = "https://github.com/golemfactory/ya-relay.git", rev = "506a678ef65893e9c0d857e4d7b8f84999790928" }
ya-relay-proto = { git = "https://github.com/golemfactory/ya-relay.git", rev = "506a678ef65893e9c0d857e4d7b8f84999790928" }

Even if proto, stack and core are not used directly.
Possible way of resolving it would be to use relative paths + versions in workspace cargo.toml and then use them in others like so:

[dependencies]
ya-relay-stack = { workspace = true }
[...]