Add a protected method
bool equals(const GeoDataGeometry &other) const
to GeoDataGeometry. It should check whether extrude and altitudeMode are equal.

Make it possible to check for equality using operator== in the following classes:
- GeoDataPoint (first check GeoDataGeometry::equals(), then the coordinates)
- GeoDataLineString (first check GeoDataGeometry::equals(), tesselate() and size(), afterwards iterate over all points and check them. If one differs, return false)
- GeoDataLinearRing (same as line string, but check isClosed() as well)
- GeoDataPolygon (first check GeoDataGeometry::equals(), isClosed(), tesselate(), outerBoundary(), each of innerBoundaries())

Add unit test method to tests/TestEquality for each of the classes. Make sure to compile Marble with the following cmake options enabled: BUILD_MARBLE_TESTS=TRUE, BUILD_MARBLE_TOOLS=TRUE. Execute tests/TestEquality and make sure no errors come up. Use tools/kml2kml to analyze errors and fix the tag writers, if needed. Submit a review request at https://git.reviewboard.kde.org with the marble group as reviewers.

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