Invoke `_initialize` method on every call if present.
In NEO3 there is no entrypoint and methods are invoked by offset,
thus `Main` function is no longer required.
We still have special `Main` method in tests to simplify them.
Allow to invoke methods by offset:
1. Every invoked contract must have manifest.
2. Check arguments count on invocation.
3. Change AppCall to a regular syscall.
4. Add test suite for `System.Contract.Call`.
We make it explicit in the appropriate Block/Transaction structures, not via a
singleton as C# node does. I think this approach has a bit more potential and
allows better packages reuse for different purposes.
Closes#913.
Provide package info in the funcScope to check if function is defined
insided an interop package. As a good side-effect bytecode for builtins from `util`
is no longer emitted.
Related #941.
