Use term StakeShuffle across the docs

[xaur]

So it turns out that CoinShuffle++ is just one part of the equation. So far I've learned that

• what ends up on the blockchain is called CoinJoin transactions
• CoinShuffle++ is a protocol and software to coordinate CoinJoins in a way to make the server trustless. It could be some other way not CSPP at all. There is no such thing as CoinShuffle++ transactions and there is nothing CSPP on-chain.
• creation of CoinJoins is integrated with Decred's Proof of Stake system in a specific way

Recent marketing discussions suggest several people are happy with the StakeShuffle term to capture all of the above and being less user-unfriendly at the same time. It was used in the press release and picked up by some news outlets (just google it). We'll be using it in Decred Journal too, unless a better term shows up and gains support.

Whatever the final term is, the incorrect usage of CoinShuffle++ is already out of the bottle. But at least we can fix some dcrdocs pages.

Places to update:

• Overview text
• How to use CoinShuffle++ text and title
• section name Privacy / CoinShuffle++ (mkdocs.yml)
• when Glossary is updated for privacy it should contain an entry for StakeShuffle (having an entry for CoinShuffle++ is ok as long as it is accurate on what it is)

[dezryth]

I will work to address this in a PR for #1151 and #1152

[xaur]

After recent discussions, it must be clarified that this issue is about using term "StakeShuffle" in more "user facing" and "simplified" places (introductions, entry points that we share to newcomers), and it should be used as a synonym to "Decred Privacy", i.e. all elements involved.

CoinShuffle++ must still be mentioned where appropriate to give it due credit, along with other involved tech.

I think the right places to mention CSPP is anywhere where we need to break down what StakeShuffle is made of, some "advanced" pages, and places that talk specifically about configuring the CSPP server used.