a77b63c569
(Part 1 was 00963afc14978b) Does the following changes visible to users: * Use panels and sub-panels for more structured & logical grouping * Re-organized options more logically than before (see images in D4148) * Use flow layout (single column by default). * New layout uses horizontal margin if there's enough space. * Change size of Preferences window to suit new layout. * Move keymap related options from "Input" into own section. * Own, left-bottom aligned region for Save Preferences button. * Adjustments of names, tooltips & icons. * Move buttons from header into the main region (except editor switch). * Hide Preferences header when opened in temporary window. * Use full area width for header. * Don't use slider but regular number widget for UI scale. * Gray out animation player path option if player isn't "Custom" Internal changes: * Rearrange RNA properties to match changed UI structure. * Introduces new "EXECUTE" region type, see reasoning in D3982. * Changes to panel layout and AZone code for dynamic panel region. * Bumps subversion and does versioning for new regions. RNA changes are documented in the release notes: https://wiki.blender.org/wiki/Reference/Release_Notes/2.80/Python_API/Preferences_API Design & implementation mostly done by @billreynish and myself. I recommend checking out the screenshots posted by William: https://developer.blender.org/D4148#93787 Reviewed By: brecht Maniphest Tasks: T54115 Differential Revision: https://developer.blender.org/D4148