Now all escaping required for the C++ code generation is done when the
.cpp/.h files are generated. Previously, only newlines were escaped
automatically. This was a) inconsistent and b) leaked c++ details into
the xml data.
In addition, the escaping is now done in one central place, harmonizing
the three previous implementations.
Pre-existing c++ escape sequences in the XML files have been replaced by
their literal equivalent so that the resulting python doc sting remains
unchanged.
* Add always zoom invariant and always on top rendering to
ViewProviderDatumCS
* Add a new utility class AxisOrigin for more efficient axis rendering.
Also exposed to python.
* Change ViewProviderPlacement to use AxisOrigin for rendering.
A single instance of AxisOrigin is shared by all
ViewProviderPlacement. Selection context is used to distinguish among
different instances.
