1. Add a new style "Tree Slim". If enabled, tree
support branches are merged more aggressively, and the support volume
is minimized.
2. Enable support style, add back Snug for normal support.
3. Remove hybrid(auto) type and use "Tree Hybrid" style to represent it.
4. Fix a bug in plan_layer_heights that may generate empty layers when
layer height is set to 0.3mm.
5. Fix a bug where no raft is generated if there is no overhang.
6. Fix the bug where no bottom interface or bottom gap is generated when
tree slim is selected.
7. Use physical distance to calc radius
Change-Id: Iacd57018ae5496cdc9acd28551c44d1c88c53fe0
29dbc77e91