dApp staking v3 - part 3 (#1036)

* dApp staking v3 - PR3

* SingularStakingInfo

* SingularStakingInfo tests

* Stake work

* Stake & lots of tests

* TODOs, renaming, improvements

* Refactoring & cleanup

* More fixes

* Rework series

* Series tests

* Minor adjustment

* stake test utils & first test

* Stake test

* stake extrinsic tests

* Era & Period change logic

* Update era/period transition in mock & tests

* on_init tests & refactoring

* Unstake & some minor improvements

* Lots of type tests for unstake

* More tests

* More types test

* Testing utils for unstake, some TODOs

* Unstake tests

* Minor adjustments

* Fixes

* Additional scenario

* Address review comments

* Correct unstake amount

* Tests