Changed folder structure for ontologies, review based changes

[Piyush13y]

This PR fixes Issue#1

Description of changes

• Changed structure for ontologies from the previous PR based on reviews and deleted redundant files.

Has the following structure now:

- forte_medical 
- ftx 
  |_ medical
      |_ __init__.py 
      |_ clinical.py

• Updated example to work with correct namespaces now.
• Modified setup.py to use find_namespace_packages() now
• Added a .gitignore file

[hunterhector]

Thanks for the fix. One thing missing is how the setup.py work (https://packaging.python.org/en/latest/guides/packaging-namespace-packages/#native-namespace-packages), we need to let it know that we use certain namespaces.

Btw, to enforce this convention and make everything consistent in the future, we probably should also adopt the same convention in Forte main repo (this should be an issue on Forte):

this includes several small steps:

1. update https://github.com/asyml/forte/blob/master/forte/ontology_specs/medical.json which in turn that package path, to make them not in the "ftx" package directly. Need to also update the usage of this (in the examples you try before, but we should search for the usage more carefully).
2. after generating the code, we remove the init file here: https://github.com/asyml/forte/tree/master/ftx
3. update setup.py according to this: https://packaging.python.org/en/latest/guides/packaging-namespace-packages/#native-namespace-packages
   • packages=find_namespace_packages(include=['ftx.*'])

The reason is that namespace packaging requires us to use the same convention everywhere, otherwise weird things would happen during import.

[hunterhector]

Consider commit a .gitignore file to skip some files, you can use this sample: https://github.com/asyml/forte/blob/master/.gitignore