Add tests & Service's Configuration has optional fields that shouldn't be optional (#4842)

Related to #4776 
Related to https://github.com/paritytech/polkadot/pull/832

To summarize the changes:
1. I did not manage to validate with types the service's Configuration. But I did reduce the possibility of errors by moving all the "fill" functions to their respective structopts
2. I split params.rs to multiple modules: one module params for just CLI parameters and one module commands for CLI subcommands (and RunCmd). Every command and params are in their own file so things are grouped better together and easier to remove
3. I removed the run and run_subcommand helpers as they are not helping much anymore. Running a command is always a set of 3 commands: 1. init 2. update config 3. run. This still allow the user to change the config before arguments get parsed or right after.
4. I added tests for all subcommands.
5. [deleted]

Overall the aim is to improve the situation with the Configuration and the optional parameters, add tests, make the API more consistent and simpler.

substrate/bin/node-template/node/src/command.rs

@@ -15,32 +15,35 @@
 // along with Substrate.  If not, see <http://www.gnu.org/licenses/>.
 
 use sp_consensus_aura::sr25519::{AuthorityPair as AuraPair};
-use sc_cli::{VersionInfo, error};
+use sc_cli::VersionInfo;
 use crate::service;
 use crate::chain_spec;
 use crate::cli::Cli;
 
 /// Parse and run command line arguments
-pub fn run(version: VersionInfo) -> error::Result<()> {
+pub fn run(version: VersionInfo) -> sc_cli::Result<()> {
 	let opt = sc_cli::from_args::<Cli>(&version);
 
-	let config = sc_service::Configuration::new(&version);
+	let mut config = sc_service::Configuration::from_version(&version);
 
 	match opt.subcommand {
-		Some(subcommand) => sc_cli::run_subcommand(
-			config,
-			subcommand,
-			chain_spec::load_spec,
-			|config: _| Ok(new_full_start!(config).0),
-			&version,
-		),
-		None => sc_cli::run(
-			config,
-			opt.run,
-			service::new_light,
-			service::new_full,
-			chain_spec::load_spec,
-			&version,
-		)
+		Some(subcommand) => {
+			subcommand.init(&version)?;
+			subcommand.update_config(&mut config, chain_spec::load_spec, &version)?;
+			subcommand.run(
+				config,
+				|config: _| Ok(new_full_start!(config).0),
+			)
+		},
+		None => {
+			opt.run.init(&version)?;
+			opt.run.update_config(&mut config, chain_spec::load_spec, &version)?;
+			opt.run.run(
+				config,
+				service::new_light,
+				service::new_full,
+				&version,
+			)
+		},
 	}
 }

substrate/bin/node-template/node/src/main.rs

@@ -7,10 +7,8 @@ mod service;
 mod cli;
 mod command;
 
-pub use sc_cli::{VersionInfo, error};
-
-fn main() -> Result<(), error::Error> {
-	let version = VersionInfo {
+fn main() -> sc_cli::Result<()> {
+	let version = sc_cli::VersionInfo {
 		name: "Substrate Node",
 		commit: env!("VERGEN_SHA_SHORT"),
 		version: env!("CARGO_PKG_VERSION"),