TUserKey and TRoleKey parsing parameters.

[nicholi]

Same functionality added as in PR for IdentityServer.v3.AspNetIdentity (https://github.com/thinktecture/Thinktecture.IdentityServer.v3.AspNetIdentity/pull/27). Contains fix for https://github.com/thinktecture/Thinktecture.IdentityManager.AspNetIdentity/issues/11

• Allow the delegate to parse TUserKey and TRoleKey to be passed as constructor argument. Makes it simple if someone does have some strange struct/other value-only parameter as their key.
• Also fixed typo error on line 63, should have been User instead of Role.
• If not passed (default), attempts best guess at pre-determined parsing functions as usual.

[brockallen]

Ok, had to merge manually. Double check for me that I got it all, please.

Thanks.

[nicholi]

Yeah looks correct. Sorry if any of that was my fault.