actlearn: decision_tree: Bug Fixes, Save and Load Functions
actlearn: decision_tree: Bug Fixes, Save and Load Functions

1. Fixes precision related bugs which cause SEGFAULT (error code 139)
2. Add Export and Load function from dict structure, the exported dict
   structure can be pickled into binary file
3. Add Graphviz directed graph (DOT) file export for visualize the
   learned tree structure

Signed-off-by: Tinghui Wang <b242afeef4efadf7acab60ba9204ad943623eea5@wsu.edu>

TinghuiWang/ActivityLearning