* Use the SDK `Client` to check whether a HS is compatible
* Remove usage of unused `WellKnown`, keep `ElementWellKnown`
* Make `HomeServerLoginCompatibilityChecker.check` return `true/false` values to distinguish non-valid homeservers from a failed check
* Use `inMemoryStore` and `serverNameOrHomeserverUrl`
* Do some cleanup of `isValid` and `isWellknownValid`
* Make the debounce for starting the search a bit higher, as checking for the homeservers seems more resource-intensive now
