write gauss fitting model for vistrails wrapper
add all three functions for vt wrap
use factory to replace individual fitting model
remove x and y from outputs
add test in test_fitting.py
add list on dict values for python 3
correction on test
DEV: Changed variance selection to be selectable list

Changed *_vary input parameters to be selectable lists instead
of simple string inputs.
Merge pull request #4 from giltis/fitting_model_vt

DEV: Changed variance selection to be selectable list
generate local coverall html, updated tests
Merge remote-tracking branch 'origin/fitting_model_vt' into fitting_model_vt
add cover folder in gitignore
clean up
Merge pull request #152 from licode/fitting_model_vt

Fitting function for vistrails wrapper