[Reviewer: Alex] Various fixes

Should be uncontroversial - fixes https://github.com/Metaswitch/sprout/issues/538. The corresponding code changes are:

https://github.com/Metaswitch/sprout/issues/700
https://github.com/Metaswitch/sprout/issues/698
https://github.com/Metaswitch/sprout/issues/697
https://github.com/Metaswitch/cpp-common/issues/165
https://github.com/Metaswitch/sprout/issues/695
https://github.com/Metaswitch/sprout/issues/694
https://github.com/Metaswitch/sprout/issues/693
https://github.com/Metaswitch/cpp-common/pull/163
How can the contact address *be* an emergency registration?