Tests integration into v0.12

[dr-orlovsky]

No description provided.

[fedsten]

Could you share the motivation of copying rgb-tests into this repository?

[dr-orlovsky]

Many reasons:

1. I can't work with git submodules. It kills my time and productivity. So approach in rgb-tests is non-working for me
2. I do not know that code and I need to copy method by method to somewhere and make them compile, step by step. Thus, I need two repos (one new to copy into)
3. Normally there are no "dedicated test repos". Tests are added to the top-level test repo and crate as tests directory. So here is the right place to have them