Move all cw20 examples to new repo

[ethanfrey]

These are not really maintained, but more examples.

Let's move all cw20-* except for cw20 and cw20-base to a new cw-tokens repo. And then let the community add lots of examples there. Those are to show ideas nothing final.

We can then focus this repo on production code to be imported by others. Those examples are nice but should not be deployed without some modifications/understanding