nlsr: Add support for sources to NamePrefixList

Added support for string sources to NamePrefixList entries.  Required was
some tweaking of the API, and refactoring usage around the codebase.

Change-Id: I44813e024a88dc1f591f427b0fad568a7d5353ab
refs: #4177
diff --git a/tests/update/test-prefix-update-processor.cpp b/tests/update/test-prefix-update-processor.cpp
index 19deaf6..32cacb5 100644
--- a/tests/update/test-prefix-update-processor.cpp
+++ b/tests/update/test-prefix-update-processor.cpp
@@ -253,7 +253,7 @@
   NamePrefixList& namePrefixList = nlsr.getNamePrefixList();
 
   BOOST_REQUIRE_EQUAL(namePrefixList.getSize(), 1);
-  BOOST_CHECK_EQUAL(namePrefixList.getNameList().front(), parameters.getName());
+  BOOST_CHECK_EQUAL(namePrefixList.getNames().front(), parameters.getName());
 
   BOOST_CHECK(wasRoutingUpdatePublished());
   BOOST_CHECK(nameLsaSeqNoBeforeInterest < nlsr.getLsdb().getSequencingManager().getNameLsaSeq());