fdo#35712 fdo#40315 fdo#40314 Autoselect trendline type

Modification of Degree or Period select trendline type
Modification of Intercept select option

Change-Id: If3a212c381061e831ee4411c8e17fbaf8ca12895
Reviewed-on: https://gerrit.libreoffice.org/6815
Reviewed-by: Tomaž Vajngerl <quikee@gmail.com>
Tested-by: Tomaž Vajngerl <quikee@gmail.com>
Reviewed-on: https://gerrit.libreoffice.org/6855
fdo#40315 Improve UI for moving average trendline

If moving average trendline is selected, show equation is
uncheked, and all options disable

Change-Id: Ic25c09b8c8410a12ac9f14cb0ba7833f304053ee
Reviewed-on: https://gerrit.libreoffice.org/6796
Reviewed-by: Tomaž Vajngerl <quikee@gmail.com>
Tested-by: Tomaž Vajngerl <quikee@gmail.com>
Reviewed-on: https://gerrit.libreoffice.org/6856
write valid dxf record, related fdo#71971

Change-Id: I99f4dfca78cc0fd5d9b947000a99f8414c2a899b
more OOXML export validation fixes, fdo#71971

Change-Id: Ic322d58817986887bbcd666ac3abc416609adf5c
make the validation tool happy

This is just fucking awesome. The MSO implementers notes mention this
attribute and point to some extended information that is either missing
or does not mention this attribute. To make it more funny the MSO
validation complains about invalid values in this attribute for our
export.

Change-Id: Iacf1a6666f9f6124106952ae19ae5d5866bc8cf1