* account: Implement IManagerForApplication calls and IAsyncContext
This implement:
- IManagerForApplication::EnsureIdTokenCacheAsync (accordingly to RE) but the Async task is stubbed.
- IAsyncContext interface (accordingly to RE).
- IManagerForApplication::LoadIdTokenCache (checked with RE, and stubbed).
I've tried some games but now they needs some `sfdnsres` calls, some other boots and crashes with other issues.
Maybe we should disable the connection somewhere to lets the game think we are offline. I have done many attempts, without success, but since the code is here now, it's better than nothing.
(I've cleaned up `using` of IGeneralService too)
Closes#629 and closes#630
* change AccountId
* Fix gdkchan's comments
* use CompletedTask
