* make spec.name() part of database_path preventing collisions
resolves#279
* add `id` field to `ChainSpec`
* add blank line for readability
* dot/cli: use spec_id in db_path
* dot/cli: make spec_id part of keystore_path
* dot/cli: make spec_id part of network_path
* add id field to poc-1.json chain spec
* dot/cli: spec_id -> chain_id
* runtime: refactor Checkable and BlindCheckable traits
* fix impl BlindCheckable for Extrinsic
* fix impl Checkable for TestXt
* fix impl Checkable for UncheckedExtrinsic
* fix tabs
* add ::Address to system::Trait since its no longer in Checkable trait
* replace tab by space in comment
* replace occurences of Checkable::check with ::check_with
* tx-pool: replace CheckedIntrinsic type alias since it now would require type param
* make more uses of Checkable compile
* adapt Executive impl to new Checkable trait
* fix that CheckedExtrinsic takes AccountId not Address as first type param
* Checkable trait: return error again since it's required in some cases
* Checkable: improve docstrings
* consistent punctuation and capitalization in docstrings
* Ctx -> Context
addresses https://github.com/paritytech/polkadot/pull/287#discussion_r200956240
* reduce trait bounds for impl Checkable for TestXt
addresses https://github.com/paritytech/polkadot/pull/287#discussion_r200839303
* use <UncheckedExtrinsic as Checkable>::Checked
addresses https://github.com/paritytech/polkadot/pull/287#discussion_r200955165
* Revert "add ::Address to system::Trait since its no longer in Checkable trait"
This reverts commit 02eb103015b833c995c9f9067aac2542bb7ce5ea.
* runtime/executive: properly fix that Address no longer in Checkable
* return `Result<Self::Checked, &'static str>` from `Checkable::check`
snd