Inner cone visualization for spotlight was added, as well as drag
handles to adjust inner and outer cone angles and fade.
Fade handle adjusts fades in order: quadratic, linear, constant.
If a specific fade value is zero, the next one in list is chosen
for adjustment.
Change-Id: I921936d9782de511558bc6c24cfa0953cce494f0
Fixes: QDS-2038
Reviewed-by: Thomas Hartmann <thomas.hartmann@qt.io>
e4b2e45ea6