When the identity provider does not provide a validity of the credentials, the Java implementation takes now + 6 months while we took now + 52/2 weeks, which is not always the same. This commit takes the approach of the Java implementation.

Instead, a client state stored at testdata/teststorage is now used.

When a problem occurs during parsing or verifying a scheme manager or any of its underlying files, this is now stored in the scheme manager struct itself instead. Invalid managers are kept in Configuration.SchemeManagers.

Instead we just branch in some functions over whether or not the session is interactive. This solves some code duplication; gives manual sessions the ability to download unknown scheme manager files on the fly, like interactive sessions; and it solves manual sessions missing some calls back to the Handler.

Change API server port to 8088

See: https://github.com/privacybydesign/irma_api_server/pull/11

* Add config -> preferences update function. Strip sentryDSN out of preferences and into a package variable.

* Typo

Manual sigrequests

Unit tests tended to sometimes fail when state from previously
(panic()'d) was still present in test storage, and when the test
storage directory did not exist. This should fix both.