Improve WritablePolygon2D and WritablePolyline

[ctrueden]

This branch makes the following improvements:

• Polygon2D and Polyline common API is now inherited from Polyshape interface.
• WritablePolygon2D and WritablePolyline common API is now inherited from WritablePolyshape interface. The WritablePolygon2D#addVertex(int, double[]) method is deprecated in favor of WritablePolyshape#addVertex(int, RealLocalizable).
• DefaultWritablePolygon2D#addVertex, DefaultWritablePolyline#addVertex and DefaultWritableRealPointCollection#addPoint now update the bounds based on the new point only, avoiding an O(n) bounds rebuild. (RealPointSampleListWritableRealPointCollection did not suffer from this issue.)
• WritablePolyshape gained an addVertices method for adding many vertices at once. This bulk operation enables the default implementations to perform better, expanding their internal storage once as appropriate, rather than doing repeated incremental expansions.
• Add methods to GeomMaths to compare Localizable and RealLocalizable positions. (Maybe these should go into net.imglib2.util.Util? What do others think?)
• The WritablePolygon2DTest code has been improved a bit.

Note that WritableRealPointCollection still does not have addPoints or removePoints methods; I considered doing them as part of this PR, but I have no immediate use case, so I've held off for now.

With these changes, it will be more feasible to pass WritablePolyshape objects as outputs into which calculated points can be injected. In particular, it will become feasible to recast ImageJ Ops's geometry operations such as geom.convexHull(Polygon2D) as computer ops rather than function ops.

[awalter17]

@ctrueden Thank you for your work on this (and cleaning up some of my tests)!

Add methods to GeomMaths to compare Localizable and RealLocalizable positions. (Maybe these should go into net.imglib2.util.Util? What do others think?)

I think these methods should go in net.imglib2.util.Util, because they seem more general than GeomMaths.

Aside from that though, I think these changes are wonderful and (pending a decision on the above) are good to merge. Thoughts @tpietzsch?

[ctrueden]

Thanks for reviewing, @awalter17. I filed imglib/imglib2#211 to add the locationsEqual methods to Util in ImgLib2 core. @tpietzsch If you like it, we can leave this PR here until it is merged and released and then update the PR accordingly. Or if not, close it and I'll put those methods wherever you deem best.

[ctrueden]

Rebased over the latest master. I also added a commit cleaning up the GeomMasks javadoc. And I removed the GeomMaths.locationsEqual methods in favor of Util.locationsEqual from imglib/imglib2#211. This PR depends on imglib/imglib2#211 being merged and released first.

[imagejan]

The build on master failed because of a typo in the javadoc here: @Link -> @link

[ctrueden]

Fixed with 07f5716162c1c95f81389a9d8df9819d17f227d7