XDGF: Add support for PolyLineTo geometry type

[komarovd95]

Implementation of POLYLINE geometry using LineTo path segments.

The code itself runs in production for a relatively long time and tested multiple times. I also used this file to test its working.

[pjfanning]

Can I ask you to test with Java 8. Neither this nor your previous PR compile with Java 8.

Issues like

/Users/pj.fanning/svn/poi/poi-ooxml/src/test/java/org/apache/poi/xdgf/usermodel/section/geometry/TestPolylineTo.java:100: error: cannot infer type arguments for java.util.HashMap<K,V>
                new HashMap<>() {{

I will fix this locally so you don't need to fix it here - but if you submit more PRs, can you ensure that they compile?

[komarovd95]

Can I ask you to test with Java 8. Neither this nor your previous PR compile with Java 8.

Issues like

/Users/pj.fanning/svn/poi/poi-ooxml/src/test/java/org/apache/poi/xdgf/usermodel/section/geometry/TestPolylineTo.java:100: error: cannot infer type arguments for java.util.HashMap<K,V>
                new HashMap<>() {{

I will fix this locally so you don't need to fix it here - but if you submit more PRs, can you ensure that they compile?

Sorry, my fault. I'll definitely check it next time