Remove bower_freeze and bower_install

[freeyoung]

• bower_install is not working with Django >= 1.9:

  File "/Users/username/.venv/venvname/lib/python2.7/site-packages/djangobower/management/commands/bower_install.py", line 8, in Command
      option_list = BaseBowerCommand.option_list + (
  AttributeError: type object 'BaseBowerCommand' has no attribute 'option_list'
  

• bower_install and bower install are confusing: https://github.com/nvbn/django-bower/issues/38

• bower_install and bower_freeze can be done via bower install and bower freeze

• bower_install and bower_freeze are undocumented: https://django-bower.readthedocs.io/en/latest/usage.html