Fix#3592. Fix#3594. The original issue asked that Data Validation be added for Xml spreadsheets. However, doing so exposed some other Data Validation problems, which are corrected along with the Xml portion.
The main other problem is that the code for `Cell\DataValidator::isValid` covered almost no possibilities. It is expanded to include all possibilities, except for Custom Types, which I will continue to think about. Many tests are added.
An obscure problem is that Xlsx Reader does not quite work properly when the Data Validation cells are beyond the high-used column or row. We use the high-used values because it is completely impractical to set all the cells in a range when an entire column or row is selected. This change causes the leftmost top cell in a range to be explicitly allocated, affecting the high-used values. It is not 100% effective, but it will be much more difficult to get into the problem situation, which I will continue to think about.
Although our expectation is that we will not see any Xml Spreadsheets using non-standard namespacing, much of the Xml Reader code is changed to use proper namespace techniques. A few areas which just had nothing to do with this change continue to use less robust techniques; I plan to address those soon after implementing this change.
One of the Data Validation types is for time of day. Testing revealed that `Shared\Date::convertIsoDate` was insufficiently robust when determining whether its input consisted of a time of day without date. It is now more robust.
oleibman