rename eos_assert to eosio_assert, implement is_account() api, and move implementation from apply_context.hpp to .cpp

Adding a few more constraints on the WASM execution environment. Some of these we’re well aware of but others are new constraints to aid performance and scalability.

* Limit initial linear memory size to 16 pages (1MB) maximum
* Limit linear memory initializers to the first page (first 64KB)
* Limit number of table elements to 1024
* Limit mutable globals to a maximum of 1KB
* Limit load/store offsets to a maximum of 1MB (matching maximum runtime size)

back to singleton for accounts, bugfixes in db api, test for trusted owner (fails because primary_lower_bound doesn't work as I expected)

fixed stale reference if the transaction meta was moved (and it was), fixed the lack of cleanup for the pending transaction metas

moved just-in-time transaction packing to `apply_context` instead of the intrinsic, added/renamed intrinsics to match precedence set by the action api, added entries in the appropriate eosiolib hpp file

- added api to update producers from wasm
- removed staked_balance objects and other deprecated code

removed the utility thread which was in charge of compiling as we were seeing locks under load and a sufficiently multithreaded version would likely need a more robust solution

Provide a more natural interface in apply_context and have wasm_interface provide the shim code to accommodate the contract API.

Fixed get_active_producers for c API passing buffer byte length and added returning the number of bytes written, so user knows how many bytes were populated.

initial draft of STL support for contract's code, doesn't work for now (STL is not in this repository)

There are a couple native methods callable from WASM where the methods expect a NULL terminated char array (a string). Validate that the string lives entirely within active pages before dispatching it. Otherwise native code could segv if given a non-null-terminated string on the end of active pages.

WASM globals are disparate from WASM linear memory. Similar to how we reset linear memory after each invocation, we need to reset globals as well.