D23585: Add color and palette APIs for Grantlee

[Volker Krause]

vkrause created this revision.
vkrause added reviewers: skelly, kde-pim.
Herald added a project: KDE PIM.
vkrause requested review of this revision.

REVISION SUMMARY
  This aims at enabling us to do the entire CSS styling via Grantlee, by
  providing access to palette colors, by offering color operations and by
  allowing to convert colors to CSS compatible strings.
  
  Most of this is fairly straightforward, the ugly one is the colorMix
  operator. I didn't find a way to do a two argument filter with both
  arguments referencing variables. Therefore it's done as a tag, which in
  turn means we can't chain it to other operations, and the output format
  is fixed. And while color mixing isn't used in the current messagelib CSS
  generation, it's heavily used in the Breeze style code (which is what I'm
  trying to follow for the itinerary plug-in at least).
  
  This isn't complete, there's more color operations in use in styling
  (such as desaturate or tint), and this still misses KColorScheme access.
  All that should be doable in a very similar fashion though, as needed.
  Using FilterExpression for the two inputs of the colorMix operator might
  also be an interesting future extension.
  
  This works with the last Grantlee release, on Grantlee master it fails
  without https://github.com/steveire/grantlee/pull/56.

REPOSITORY
  R77 PIM: Grantlee Theme

BRANCH
  master

REVISION DETAIL
  https://phabricator.kde.org/D23585

AFFECTED FILES
  CMakeLists.txt
  autotest/CMakeLists.txt
  autotest/data/themes/color/color.html
  autotest/data/themes/color/color.testdesktop
  autotest/data/themes/color/color_expected.html
  autotest/grantleethemetest.cpp
  src/plugin/CMakeLists.txt
  src/plugin/color.cpp
  src/plugin/color.h
  src/plugin/kdegrantleeplugin.cpp
  src/plugin/palette.cpp
  src/plugin/palette.h

To: vkrause, skelly, kde-pim
Cc: fbampaloukas, dvasin, rodsevich, winterz, vkrause, mlaurent, knauss, dvratil
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