* Support Border for Charts
All chart linestyles will be supported for Chart Border. Also add fill color for Chart. Also 'nofill' for Axis (allows suppressing of vertical axis line). These are demonstrated in sample 32_readwriteChartLine5, and a new unit test member is added. This addresses some vague problems added to issue #1797 over 8 months after it was closed; there is still at least one problem, much more complicated than the 2 being addressed in this PR.
* Handle Legend Borders in Same Way as Chart Borders
Consistency is good, and the implementation of Chart Borders offers more possibilities than the implementation of Legend Borders had. Since Legend Borders hasn't made it to a release yet, there is no need for deprecations.
* Allow Color and Effects on Data Points on Chart Axis
Fix#3414. There had been no way to do this. It is now supported via a new AxisText class, which derives from Properties, and has FillColor and effects (glow/shadow/softEdges) properties. The code changes in chart sample 33_Chart_create_scatter2 illustrate usage.
* Minor Performance Improvement
May also get rid of Scrutinizer complaint.
* Eliminate New Spacing Patch
No need for it.
* Add Legend Formatting to Change
Much in common with Data Point formatting.
Jpgraph does not use namespaces. Neither do the Samples members of this project. As a result, Scrutinizer complains about 13 cases of `use PhpOffice\PhpSpreadsheet\Chart\Legend;`, since this theoretically could cause the use of two different Legend classes in the empty namespace. It suggests using a class alias for Legend, which this PR does in every applicable case. It is a regrettable problem, but it is easy to fix.
All chart examples passed the displayBlanksAs parameter as 0 instead of 'gap'.
I added a constants EMPTY_AS_GAP, EMPTY_AS_ZERO and EMPTY_AS_SPAN to the
DataSeries and then change all chart samples to use this new constant.
Fixes#1337Closes#1448
MarkBaker
oleibman
Adrien Crivelli
Chris Wolcott