change from SpelMessages to SpelMessage. Changed exception getter to getMessageCode() from getMessageUnformatted

changed to [] from {} for projection and selection (including first and last selection).  addresses the problem of clashes with template prefix/suffix

SPR-5673: more intelligence in TemplateAwareExpressionParser.  Supports prefix/suffix escaping and nesting of prefixes/suffixes

more tests - about 82% coverage now.  focused on testing reflection helper since it is rather complex.  some asserts also added.

objects flowing around in expression evaluation are now TypedValue's - these carry generics info, used for conversions.

design change - no longer surfacing typeDescriptor through property accessor.  conversion done internally in property write() code