Enhanced KML support

[Joern Ungermann]

The current KML overlay widget solved several practical issues but has several shortcomings:

• it does not support several features of KML
• colour of overlay may not be configured
• zorder of the overlay may not be configured, potentially causing undesired behaviour.
• only one overlay is possible

[Reimar Bauer]

Restructured Patch/overlay plotting so less calls to path interactor are required and satellite overpass and kml overlay is more consistent.

See issue #98

→ <<cset 819ef1219ef7>>

[Reimar Bauer]

KML: Add LineString support and ability to change colour of overlay

In addition, the name of Point placemarks is added as text. Added two basic sample files to the docs/samples folder for testing.

See Issue #98

→ <<cset d97249a26125>>