This implements refresh tokens, as defined by MSC2918
This MSC has been implemented client side in Hydrogen Web: vector-im/hydrogen-web#235
The basics of the MSC works: requesting refresh tokens on login, having the access tokens expire, and using the refresh token to get a new one.
Signed-off-by: Quentin Gliech <quentingliech@gmail.com>
The hope here is that by moving all the schema files into synapse/storage/schema, it gets a bit easier for newcomers to navigate.
It certainly got easier for me to write a helpful README. There's more to do on that front, but I'll follow up with other PRs for that.
