Rework list ending data paths

There are now four modes to NodeParser. This mode is specified by the
NodeParserMode enum via a template argument.

Modes:
SchemaNode: will parse schema nodes.

CompleteDataNode: works exactly as the dataNode_ parser before. It will
parse data nodes.

IncompleteDataNode: works the same as CompleteDataNode, but allows
parsing a list without keys.

CompletionsOnly: in this mode, the parser only creates completions, and
doesn't do any actual parsing. This mode is needed when parsing a path
ending with a list without keys, with a trailing slash.
Example: /module:list/
After the path fragment and the trailing slash are parsed, no more node
parsing happens (because there's no more input). However, I still need
to generate completions. That's when I need to use CompletionsOnly.

PathParser now also has modes, they are similar to the NodeParser modes.
They are used to state what kind of path is supposed to be parsed.

Change-Id: I65b6de45c452ece37002a5cfe4048b9042562d2a
diff --git a/tests/ls.cpp b/tests/ls.cpp
index 93ec75b..6d70414 100644
--- a/tests/ls.cpp
+++ b/tests/ls.cpp
@@ -9,6 +9,7 @@
 #include "trompeloeil_doctest.hpp"
 #include "ast_commands.hpp"
 #include "parser.hpp"
+#include "pretty_printers.hpp"
 #include "static_schema.hpp"
 
 TEST_CASE("ls")