TopLevelStorage dependency injection

[qalisander]

Description

High Level

• fixes multi level inheritance (like 3 or more level of contract inheritance).
• allows to remove #[borrow] attributes tottaly (currently borrow attributes left for compatibility reason).
• lets to retrieve mutable and immutable references to a contract laying beneath struct that implements TopLevelStorage.
• can fix Unable to declare non #[entrypoint] struct with #[borrow] and generics #107 and help to Storage access issues with multi-level inheritance #106

Low Level

• TopLevelStorage got two additional functions to retrieve inner laying type of contract by generic param <S>.

• A new trait StorageLevel exposes two similar functions that just returns optional reference to the type <S>.

• StorageLevel implemented by every type that can exist in contract storage same as StorageType. Simple storage types implementation returns just None since we're not expecting them to store inherited contract.
• Contracts implement StorageLevel within solidity_storage macro. Implementation checks that type of self is T if so reference will be returned (unsafe reference cast). Since every storage type implements StorageLevel trait then we can call same functions in every field recursively.
• We can remove BorrowMut constraint from the router trait and use our newly created functions to retrieve references to inner contracts. This example with inheritance of three is working now.
• #[borrow] attributes will generate Borrow and BorrowMut bindings still but basically there is no need in them.

Compatibility

• generically typed contracts should have generics restricted by 'static lifetime. (example)

Checklist

• I have documented these changes where necessary.
• I have read the DCO and ensured that these changes comply.
• I assign this work under its open source licensing.