* SpawnNamed: add new trait methods

Signed-off-by: Andrei Sandu <sandu.andrei@gmail.com>

* Implement new methods

Signed-off-by: Andrei Sandu <sandu.andrei@gmail.com>

* cargo fmt

Signed-off-by: Andrei Sandu <sandu.andrei@gmail.com>

* SpawnNamed: add new trait methods

Signed-off-by: Andrei Sandu <sandu.andrei@gmail.com>

* Implement new methods

Signed-off-by: Andrei Sandu <sandu.andrei@gmail.com>

* cargo fmt

Signed-off-by: Andrei Sandu <sandu.andrei@gmail.com>

* New approach - spaw() group param

Signed-off-by: Andrei Sandu <andrei-mihail@parity.io>

* Update traits: SpawnNamed and SpawnNamed

Signed-off-by: Andrei Sandu <andrei-mihail@parity.io>

* Update TaskManager tests

Signed-off-by: Andrei Sandu <andrei-mihail@parity.io>

* Update test TaskExecutor

Signed-off-by: Andrei Sandu <andrei-mihail@parity.io>

* Fix typo

Signed-off-by: Andrei Sandu <andrei-mihail@parity.io>

* grunt work: fix spawn() calls

Signed-off-by: Andrei Sandu <andrei-mihail@parity.io>

* cargo fmt

Signed-off-by: Andrei Sandu <andrei-mihail@parity.io>

* remove old code

Signed-off-by: Andrei Sandu <andrei-mihail@parity.io>

* cargo fmt - the right version

Signed-off-by: Andrei Sandu <andrei-mihail@parity.io>

* Implement review feedback

- use Option group name in SpawnNamed methods
- switch to kebab case
- implement default group name
- add group name to some tasks

Signed-off-by: Andrei Sandu <andrei-mihail@parity.io>