ParserItem: differentiate between input type and internal data type

Differentiate between the input type, as specified in the json configuration
file, and the internal native type used to store data. This is a many-to-one
mapping, where e.g. both the input types STRING and RAW_STRING map to the
internal datatype std::string.

Additional changes:

 - Have removed several ParserItem() constructors.
 - The size_type::SINGLE is default for a ParserItem, and not set explicitly in
   the generated ParserKeywords.cpp file.
 - Have removed a call to boost::lexical_cast<> - just use std::to_string()

tests/parser/DeckTests.cpp

@@ -517,7 +517,7 @@ BOOST_AUTO_TEST_CASE(get_byNameNonExisting_throws) {
 }
 
 BOOST_AUTO_TEST_CASE(StringsWithSpaceOK) {
-    ParserItem itemString("STRINGITEM1", "" );
+    ParserItem itemString("STRINGITEM1", ParserItem::itype::STRING);
     ParserRecord record1;
     RawRecord rawRecord( " ' VALUE ' " );
     ParseContext parseContext;