Polynomial and moving average regression lines for chart

Hi,

I have implemented the polynomial and moving average regression curves
(trend lines) for chart. I have pushed the changes to a feature branch
"feature/polynomialregression" so please test it if you are interested. The
work is still ongoing but I want some feedback.

Currently implemented is:
- calculating of polynomial and moving average curve
- limited the curve calculation to min and max X value.
- properties degree and period for regression curve
- added extrapolation
- extended the "trend line" dialog (but it would be better to convert it to
the new dialog infrastructure but this is a lot of work)

Still missing:
- intercept
- finish changes to dialog
- changing import/export filters to support
- revise the proposal to extend ODF

I have made some changes to the IDL files so probably this is an API change
(It is my first time changing a IDL so I don't know what to do in this
case). Can somebody take a look at it?

The enum ChartRegressionCurveType
("offapi/com/sun/star/chart/ChartRegressionCurveType.idl")
represents the various types of regression lines. Polynomial type was
already in (however it was deprecated) but I also need to add
MOVING_AVERAGE type. If I add it, compilation fails - do I have to do
something else? ChartRegressionCurveType is only used in
"chart2/source/controller/chartapiwrapper/WrappedStatisticProperties.cxx"
and it does not influence the current functionality (but might be a problem
with filters).

Any suggestions/opinions welcome.

If I will progress fast enough I will also propose this as a late feature
for 4.1 however there were quite some changes.

Regards, Tomaž