Add warning/explainer with checkbox during name purchase

We need to make it clear to users that they are burning bitcoin and racing other users to buy names. They’re not buying names from Blockstack PBC or any other entity (this is decentralized after all!)

Let’s do this by adding this language with a checkbox to the name registration process:

Proposed language:

I understand by registering a name:
* I am racing other users to register this name by burning bitcoin
* If someone registers the name before me, the bitcoin my computer has burnt in this process will still be gone.  
* No bitcoin from this process goes to Blockstack PBC or any other entity.

Feel free to improve on this language.

Any pull request for this issue should have corresponding tests.

[kantai]

My feelings on this are that we should separate our treatment of this into solving two different problems

1. Informing users of the risks of registration (it’s a race, and someone can win, and the loser has still burnt bitcoin) and the process (your computer is doing 2 bitcoin transactions with addresses you control, the burnt bitcoin doesn’t go to us)

2. Usage agreement - This is a usage policy that seems to be tied to liability for use of the software. this is a legal decision (that probably interacts with software licensing), that I think should probably be consulted with lawyers before we add a lot of legal text to user’s interaction with the product.

[jackzampolin]

Yeah. I think we also need a good simple explanation of the name registration process and be able to link to here as well. Something like

There are 2 transactions for each name registration: NAME_PREORDER and NAME_REGISTRATION. The preorder submits a hashed version of your name to the BTC blockchain and reserves it for you. This prevents front-running, i.e. someone paying higher fees so their NAME_REGISTRATION transaction is completed first. The costs are estimated costs based on a fee api and the amount of BTC that needs to be burned for the specific name.