Implement generalized memory subsystem

[derzhavin3016]

The task is to implement generalized memory, which can store/load bytes on addresses. Initial implementation was already provided, but we need to extend it a bit. (E.g. we should reduce actual memory consumption m.b. via using page-based approach)
Also, it's better to provide some useful features in addition to what we already have:

1. fillBlock(addr, size, value) -> to fill specified range with specified value
2. Associating permissions with memory range (RWX) in order to support SMC (Self-modifyng code)