Fix markers for charts

1. In 2007 documents we handled only auto-markers for charts but not symbol-markers like at the series.
2. In 2007 documents we completly ignored any marker defined for a series cause we where checking for the internal used methodname as element-name (c:serMarker rather then c:marker).
3. In 2007 documents we overwrote any explicit to "None" set marker with the global chart marker definition making it impossible to activate globally markers and turning them off per series.
4. The code to handle auto-markers in 2007 documents was completly broken too (the important condition to check if it's the correct element was just commented out resulting in us applying auto-markers to all and everything as soon as there was an element in the hierarchy which had a "val" atribute set to true.

All those cases are fixed with this commit now.