- MergeCellsInRow - allow for merging the rows where the columns don't match (for instance, merge the last column of a row with 6 elements and a row with 3 elements will merge the last column of the row with too few elements)
- this is a specific case that I needed... others may need it as well, but I've got a separate branch with this change so it's up to you 

Container.cs (and baseclasses)
- Moved PackagePart to the base class - found an issue where images in a table contained in the header or footer wouldn't display, this keeps track of what part of the doc and passes it to child things, (like inserting a table to a paragraph in the footer will have the correct part)
- Add a deep search for paragraphs.. This is to find a bookmark within a textbox or other art.. since a paragraph will wind up with a child paragraph.. (if you are searching for a bookmark like that the second one is the "right" one)