Extract outOfBounce method
Prevent to go next when borderBehavior is bounce; Disable loop and autoScrolling when slides count is 1
Disable autoScrolling and loop when slide count is less than 2
Finished the loop problem, but there might exist two other issues:
1. when there are two slides, it won't work well
2. the logic seems too complicated
Fix a bug when loop mode is selected, bgImage would not change