New console scripts for manipulating page objects

New console scripts for manipulating page objects:

"seleniumbase" ...

+ "extract-objects"

  Usage:
           seleniumbase extract-objects [SELENIUMBASE_PYTHON_FILE]
  Output:
           Creates page objects based on selectors found in a
           seleniumbase Python file and saves those objects to the
           "page_objects.py" file in the same folder as the tests.

+ "inject-objects"

  Usage:
           seleniumbase inject-objects [SELENIUMBASE_PYTHON_FILE]
  Options:
           -c, --comments  (Add object selectors to the comments.)
                           (Default: No added comments.)
  Output:
           Takes the page objects found in the "page_objects.py"
           file and uses those to replace matching selectors in
           the selected seleniumbase Python file.

+ "objectify"

  Usage:
           seleniumbase objectify [SELENIUMBASE_PYTHON_FILE]
  Options:
           -c, --comments  (Add object selectors to the comments.)
                           (Default: No added comments.)
  Output:
           A modified version of the file where the selectors
           have been replaced with variable names defined in
           "page_objects.py", supporting the Page Object Pattern.

           (seleniumbase "objectify" has the same outcome as
            combining "extract-objects" with "inject-objects")

+ "revert-objects"

  Usage:
           seleniumbase revert-objects [SELENIUMBASE_PYTHON_FILE]
  Options:
           -c, --comments  (Keep existing comments for the lines.)
                           (Default: No comments are kept.)
  Output:
           Reverts the changes made by "seleniumbase objectify" or
           "seleniumbase inject-objects" when run against a
           seleniumbase Python file. Objects will get replaced by
           selectors stored in the "page_objects.py" file.