Refactoring of UsedChunkList

## Brief feature description

This whole list is error prone, uses the STL even though it does not have to use it (we should use here a ``cxx::vector``) and it is not tested.

## Detailed information

- [x] separate declaration and implementation
- [x] add unit tests
- [x] ~~use ``cxx::vector`` instead of ``std::array``~~ see https://github.com/eclipse-iceoryx/iceoryx/issues/623#issuecomment-803986280
- [x] ~~store sharedChunks? (see https://github.com/eclipse-iceoryx/iceoryx/pull/618#discussion_r597591727)~~ see https://github.com/eclipse-iceoryx/iceoryx/issues/623#issuecomment-803986280
- [ ] change signature of ``remove`` to ``mepoo::SharedChunk remove(const mepoo::ChunkHeader& chunkHeader)``
- [ ] decide if the `UsedChunkList` should behave like a `Set` and reject to take the same data a second time