Improve error handling/reporting

• Splash screen now shows package initialization

• Classifying log levels
  • debug 10 (cannot be accessed by setting loglevel)
  • log(info) 20
  • warning 30
  • critical 50

• ~800 print statements in VisTrails + 200 commented ones

• Translating issues
  • core/upgradeworkflow.py
    • debug.critical('Package cannot handle upgrade request. VisTrails will attempt automatic upgrade.') - Should it be critical?