In curves.cpp: fixed crucial error in Parabola

Also working on LeafDistribution class.
Light competition model & tree support partially

Fixed bug in Parabola, added the appropriate integration functions for
LeafDistribution, added slew of properties, partially finished support for
trees (testing needs to be finished)
Cleaned up unused files

Edited .gitignore, removed copies and log files.
Fixed serious bug in LeafDistribution
Nearly fully implemented trees

Changes include:
LAI function no longer accounts for delta biomass in LAI calcs
light competition is implemented.
The testing suite now includes a multi-plant function
Testing suite logs are all output in the directory logs/
Leaf shed is better (issue #9)
Updated Excel spreadsheets