Replace allocator with freeing-bump allocator (#1656)

* Link substrate issue tracker in panic

* Replace allocator with freeing-bump allocator

* Revert me: Panic on double allocate/free

* Revert me: Add shallow benchmark for a first impression

* Revert "Revert me: Add shallow benchmark for a first impression"

This reverts commit 5f0d4df3.

* Revert "Revert me: Panic on double allocate/free"

This reverts commit a114df7d.

* Rename heap to FreeingBumpHeapAllocator

* Rename heap.rs to allocator.rs

* Use sandbox heap

* Move functions

* Move variables into constructor

* Revert "Move variables into constructor"

This reverts commit f46fa0d0.

* Remove unnecessary casts

* Add comment for new parameter

* Improve typing

* Move variables into constructor

* Avoid dynamic allocation

* Remove unused variables

* Revert "Link substrate issue tracker in panic"

This reverts commit 32dfa1d0.

In the meantime this was fixed in https://github.com/paritytech/substrate/pull/1667.

* Improve naming

* Only assert in debug mode

* Remove dynamic allocation