fixed tree test
changed repo url in setup file
Added py4j info to readme
Improved py4jconnector and put it in separate module
renamed package from geogit to geogitpy
changed how null id is used
Better error/exception handling

also some minor fixes
implemented support for progress in py4jconnector.py
some code cleaning
fixed log method in case of empty repo
added tests
Improvements on the Repository class and both cli ad py4j connectors

some additional tests