#37 jbrowse_handler init fails with unvalid workspace in cfg

[Jean-Frédéric]

At launch time (when executing rnaspace_on_web), jbrowse_handler.__init__ fails when workspace_directory is defined in the config file rnaspace.cfg but does not exist (ie method get_storage_directory returns None)

The jbrowse_handler.__init__ should at least raise a meaningful error.

Steps to reproduce:
*Set the workspace_directory in cfg/rnaspace.cfg to a nonexistant path (actual state after a fresh install)
*Execute rnaspace_on_web

Traceback (most recent call last):
File "./rnaspace_on_web", line 120, in <module>
main()
File "./rnaspace_on_web", line 97, in main
root = rnaspace_controller()
File "/home/jeanfred/Workbench/rnaspace_dir/rnaspace_sources/rnaspace/rnaspace/ui/web/controller/rnaspace_controller.py", line 73, in __init__
self.predict = predict_controller()
File "/home/jeanfred/Workbench/rnaspace_dir/rnaspace_sources/rnaspace/rnaspace/ui/web/controller/predict/predict_controller.py", line 31, in __init__
self.model = predict_model()
File "/home/jeanfred/Workbench/rnaspace_dir/rnaspace_sources/rnaspace/rnaspace/ui/web/model/predict/predict_model.py", line 34, in __init__
self.sm = software_manager()
File "/home/jeanfred/Workbench/rnaspace_dir/rnaspace_sources/rnaspace/rnaspace/core/prediction/software_manager.py", line 39, in __init__
self.data_m = data_manager()
File "/home/jeanfred/Workbench/rnaspace_dir/rnaspace_sources/rnaspace/rnaspace/core/data_manager.py", line 92, in __init__
self.jbrowse_handler = jbrowse_handler()
File "/home/jeanfred/Workbench/rnaspace_dir/rnaspace_sources/rnaspace/rnaspace/dao/jbrowse_handler.py", line 45, in __init__
os.symlink(self.config.get_storage_directory(), os.path.join(os.path.dirname(os.path.abspath(__file__)), "../ui/web/ressource/jbrowse/data"))
TypeError: coercing to Unicode: need string or buffer, NoneType found