A handful of fixes

[deepakunni3]

Following issues are resolved via this PR,

• Proper and safe parsing of YAML in settings.py
• Add shebang line to app.py to have the app compatible with Werkzeug 0.15.0 (Fixes #260)
• Invert subject and object in bioentity/anatomy/<id>/genes route
• Use proper subject and object category in bioentity/genotype/<id>/model route
• Remove unused methods from bioentity.py
• Fix routes with taxon constraints
  • bioentity/phenotype/<id>/gene/<taxid>/ids
  • bioentity/anatomy/<id>/gene/<taxid>/ids