backported r293 from trunk, correctly check for multihead_mode, fixes LP: #331369
backported fix for LP:#356659 from trunk
backported fixes for LP: #338483 and LP: #356913
backported r300 from trunk, extend layout-fallback-behaviour for icon-only -> summary-body or summary, fixes LP: #357070
backported r313 from take2, disconnect any remaining bubbles when deleting the stack, avoids crash in unit tests
backported r315 from take2, init GError pointers
backported r310 from trunk, tweak bevel/gradient of value-indicator rendering, fixes LP: #338215
backported r312 from trunk, trying to better match the colors of the gauge-bar
backported r314 from trunk, change interpolation-filter from GDK_INTERP_HYPER to GDK_INTERP_BILINEAR, fixes LP: #364038
backported r315 from trunk, fixes LP: #364664
backported r318 from trunk, fixed a compiler warning hinting that dereferencing type-punned pointer will break strict-aliasing rules