Bug fixes and more

Work on DecTree
- Incorportated number of giving up attempts into tree
- To add: stability, inclination to change
- Need to get a more gradual change

Bug Fixes:
- Added new attributes to constructor for BaseHuman when importing from
a GraphMLfile.
- Added attribute to graphML exporter method within BaseHuman
- GraphML is now correctly imported/exported.

Notes:
- Might start running some simulations and analysing them soon.