ABI Support for JS library (#454)

* added abi files

* Temporarily disable linter for require() warning

* Update tests for ABI types

* Minor import change

* Remove separate encode file

* Add basic encoding tests

* Enforce Bigint args in uint/ufixed types

* Fix linter errors

* Fix more linting errors

* Address PR comments

* Add decoding functions and tests

* Fix chrome test errors by disabling crypto

* Address PR comments and try to see if we can resolve Travis errors

* Resolve circular dependencies in tests

* Change exports, naming and file structure

* Change bigint literals to BigInt()

* Remove more bigint literals

Co-authored-by: shiqi.zheng@algorand.com <shiqi.zheng@algorand.com>

Author: algochoi