fix: irmaclient now updates its credential instances if new attributes were added by the scheme manager

Updated noauth description to specifically state that it will cause server to reject authenticated requests.

Changed UpdateSchemes to run ParseFolder only when new schemes were actually downloaded, based on suggestion by Sietse.

fix: Stopped keyshare code from paniccing when getCommitments failed for reasons other than missing pin-check.

Within a session request, inner conjunctions requesting specific attribute values
used to be serialized to a map. JSON and Go maps are however unordered, and the
order matters: if the requested attributes are received in a different order then
the session will fail. Inner conjunctions using values are now serialized using
the default Go serializer, resulting in a list of requested attributes with their values.

Fixes #43

Within an inner conjunction of a session request, distinct attributes that come
from the same credential type must always be adjacent. This is now enforced in
the irmaclient and server packages when receiving session requests.

When passing --server to irma session, it would erroneously complain about
--url also being set.

fix: irma server now shows error message when invalid requestor json is passed using flag or env var

Fixes #38

Fixes #37

In particular, combined issuance sessions in which 2 or more attributes are
requested from one particular credential type, due to a miscalculation during
verification of the attributes.

Fixes #36