TOSCA parsing and validation error messages should include source filename and line number

[aszs]

TOSCA parsing and validation error messages should include source filename and line number. We have the original parsed yaml nodes elements available we just need to preserve that info all the way down to where the exception is raised.

A sketch:

1. Make yamlloader.py saves the file name in addition to the base_dir.

2. Update make_map_with_base() in merge.py to preserve the CommentedMap's lc attribute.
   From https://yaml.readthedocs.io/en/latest/detail.html: "collection objects (when read in via RoundTripParser) have an lc property that contains line and column info lc.line and lc.col. Individual positions for mappings and sequences can also be retrieved (lc.key('a'), lc.value('a') resp. lc.item(3))"

   lc = getattr(doc, "lc", None)
   ...
   if lc is not None:
   map.lc.line = lc.line
   map.lc.col = lc.col

3. Add a near class attribute to ExceptionCollector and update the ctors for the base TOSCA element classes to set their tpl instance to that class, e.g. EntityTemplate could add:

    ExceptionCollector.near = (self, self.entity_tpl)
   

4. Add a line like self.near = ExceptionCollector.near to TOSCAException ctor

Now we have enough info to augment the error message with a sentence like "error in near line n in file f

[aszs]

I didn't see lc on the CommentMap objects, not sure why... So as a hack I'm just assigning help for messages to ExceptionCollector .near in a few place in the parsing process, just search for "near" in tosca-parser.