Bug fixes
1. In QC, retain_only_1st_root replaced the ref of the SWC dataframe, the steps following would do make no modification on the original object.
Changed features
1. In QC, adjusting branches with children more than 2 needs segment finding no more, and weighing by subtree length instead of only child segment.
2. Remove the result dir in modeling classes.
3. Use a recursion decorator so that recursion limit needs no change any more, and there will be no overflow.
4. Recursion functions are refactored, too.
5. ccf_atlas module is made more clear.
6. SWC reading can have more features in specification.
7. A new swc util to get a subtree node list under a node.
Others
1. Examples are updated.
2. Sample data location moved.