Convert unnecessary storage item to static. (#3093)

* Convert unnecessary storage item to static.

* Polish

* 6 second blocks.

* Compile fixes

* Bump runtime

* Fix

* Another fix

* Import `srml_support::traits::Get`

* Export MinimumPeriod from `decl_module!`

* Remove `config` from Timestamp

* Clean up warnings

substrate/srml/session/src/mock.rs

@@ -109,6 +109,7 @@ pub fn set_next_validators(next: Vec<u64>) {
 pub struct Test;
 parameter_types! {
 	pub const BlockHashCount: u64 = 250;
+	pub const MinimumPeriod: u64 = 5;
 }
 impl system::Trait for Test {
 	type Origin = Origin;
@@ -125,6 +126,7 @@ impl system::Trait for Test {
 impl timestamp::Trait for Test {
 	type Moment = u64;
 	type OnTimestampSet = ();
+	type MinimumPeriod = MinimumPeriod;
 }