Append constructor args to runtime bytecode

[palinatolmach]

As identified by @PetarMax, we were not appending arguments to init bytecode when executing constructors taking inputs as we should. This PR

• adds a new property, encoded_args, to Constructor class, which returns concatenated ABI-encoded arguments based on constructor's inputs
• if the function being executed is a constructor, appends those arguments to the init bytecode and insert the result into the <program> cell in the initial CTerm and adds the corresponding type constraints
• adds a test, ConstructorArgsTest.test_constructor_args that exercises a constructor with two symbolic arguments

There're a few follow-ups to this PR:

• we need to support NatSpec comments for specifying length of dynamically sized types
• further refactoring of init_cterm arguments will be included in CSE: Include symbolic contracts corresponding to contract fields into accounts #600
• there's some repetition in Method and Constructor structure and input processing, with the opportunity for factoring out common logic (I've made an attempt here Refactoring flattening for dynamic types in rules #542, but didn't have enough time to update this PR or do it properly yet)