* Add Support to Chart/Axis and Gridlines for Shadow
Continuing the work from #2865. Support is added for Shadow properties for Axis and Gridlines, and Glow and SoftEdges are extended to Gridlines. Tests are added. Some chart tests are moved from Reader/Xlsx and Writer/Xlsx so that most chart tests are under a single directory.
This is a minor breaking change. Since the support for these properties was just added, it can't really affect much in userland. Some properties had been stored in the form which the XML requires them rather than as the user would enter them to Excel. So, for example, setting the Glow size to 10 points would have caused it to be stored internally as 127,000. This change will store the size internally as 10, obviously making the appropriate conversion when reading from or writing to XML. This makes unit tests much simpler, and I think this is also what a user would expect, especially considering the difficulties in keeping track of the trailing zeros.
* More Tests
Confirm value change between internal and xml.
* Still More Tests
Add a little more coverage, and use a neat trick suggested by @MarkBaker in the discussion of PR #2724 to greatly simplify MultiplierTest.
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