[QGIS-Developer] QGIS Grant "Add consistency to UI controls" complete

[Nyall Dawson]

Hi all,

Just a quick notice to advise that the work sponsored by the QGIS
grant program on "adding consistency to UI controls" is now complete
and merged into master. The following tasks were done as part of this
work:

- All API regarding transparency/opacity/alpha was standardised to
setOpacity() and opacity(). The methods take a double value between 0
(transparent) and 1 (opaque), keeping consistency with the Qt API.
- A new widget QgsOpacityWidget was created, and is now used
everywhere through the UI where opacity is set. This ensures
consistent behavior and look for opacity controls everywhere.
- Rotation has been standardised in the API and UI, so now rotation is
always applied clockwise. All rotation widgets have been updated so
they accept values from -360 to 360.
- 2.x Projects with labeling using rotation and data defined rotation
are transparently upgrade upon opening in 3.0
- Scale APIs have been made consistent throughout the QGIS API. The
confusing mix of scale denominators vs real scales has been removed,
with everything now operating on scale denominators. The behaviour of
all scale range calls is standardised with a common meaning for
min/max scales (and explicit api documentation regarding this)
- All scale controls now use the standard scale widgets for
consistency across the UI
- Labeling now uses the same definition for min/max scale as the rest
of the UI, and existing projects are transparently upgraded on opening
in 3.0.
- Fixed most outstanding bugs relating to scale usage, including bugs
breaking the rule based scale limits

Thanks to the QGIS PSC and project donors for sponsoring this work and
allowing it to proceed!

Regards,
Nyall