Remove OIDCPSessionContext.cs from project file
Allow tests for German language computers

Some tests depend on English language exceptions. This is partially
fixed to also handle German language exceptions.
Fix empty values or parameter names in OpenIdConnectMessage constructor

The KeyValuePair constructor (which is used to handle post requests)
cannot handle empty names or values correctly (e.g. &xx=xx is ok, &= is
not). IE11 passes those form parameters in case of <input> elements
without name attribute,