Rationale:
- there was a lot of large objects passed by value, so potentially
there's a speed bump from this
- even for implicitly shared classes like QString/QList there's still
a (small) cost for copying the objects when there's no reason to
- it's the right thing to do!
- Rectangle, square, circle and ellipse generated symbols
- SVG background via new symbology, so uses cache
- Add new gui class QgsSvgSelectorWidget, symbol selector setup culled from symbologyV2
- Does not include any associated data defined mappings, yet
- Does not auto-search for missing SVGs, yet
- Caveat: does not currently account for background size in PAL collision calculations (overlaps occur)
- Allow direct update of QgsColorButton background
- Add option to Options for live color chooser support (QgsColorDialog)
- Add ability to define whether QgsColorButton accepts live updates (default: true)
- Move QgsColorButton to single subclass of QPushButton
- Show different button types relative to whether button has text
- Add transparent checkerboard background for chosen colors with alpha < 255
- Fix triple-modal window issue for Mac (with regards to using native color dialog)
- Composer item frame now supports transparency
- Composer item background transparency support moved to color dialog
- Composer composition grid now supports transparency
