1. change base pattern "None" to "Hollow", and add an icon image
2. fix a bug of not initializing m_highest_overhang_layer
3. fix a bug where normal(auto) with Tree* styles won't generate any
supports.
4. add popup message when selecting support material for interface.
5. draw connected loops when wall count is larger than 1
Change-Id: I7ea211d2971b25c65724bb10d0f6cf6e0b68c6a1
(cherry picked from commit 4c1ae7f937239fc3e1397ec2cb3b290d886bb0f0)
