* 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.
* Add Support to Chart/Axis for Glow/SoftEdges
Chart is very under-covered in unit tests. I was hoping to just add some tests and be done with it, but that just won't suffice - many code changes are required. Adding Glow properties for Axis turned out to be a real mixed bag - no support in Xlsx/Reader at all, support in Xlsx/Writer ... for the X-axis only. So we'll just inch forward in many stages.
This change does not address other Axis properties (Fill, Shadow, Line, LineStyle, and maybe others, and their sub-properties). On my to-do list.
GridLines, and maybe other Chart objects, also should support these properties. This change does not address those. On my to-do list.
No support is added for spreadsheet formats other than Xlsx.
* Refactoring
This should make the code easier to follow, and I hope it will also be extensible to other object types (e.g. GridLines).
* More Refactoring
Make scheme/srgb easier to handle.
* Fix Typo
In a very rarely used function.
oleibman