[bugfix] fix bugs introduced by #78

#78 (closed) introduced several bugs. this fixes them

BUG 1:

• channelRepososotory#resolveSenderType and #resolveSenderLanguage both produced null subscriberPhoneNumber/publisherPhoneNumber by improper usage of `lodash#times``
• fix by using times properly (calling a lambda) and introduce unit tests for these functions

BUG 2:

• registrar.channel.create calls dispatcher.messenger.welcomeNewPublisher, which expects a value for language (which we do not have yet) to pass to messagesIn
• fix by making messagesIn default to default language messages if no language provided

BUG 3:

• find-and-replace elimination of messageTypes prefix in dispatcher.messenger unintentionally eliminated signal.messageTypes prefix, causing all signald messages to have no type, causing signald to throw NPEs
• fix: reintroduce signal.messageTypes namespace (and give it a sdMessageTypes aliases to make it harder to make this mistake)