[Refactor] Converge Pipeline and App classes (#1021)

Co-authored-by: Deven Patel <deven298@yahoo.com>

embedchain/__init__.py

@@ -2,10 +2,9 @@ import importlib.metadata
 
 __version__ = importlib.metadata.version(__package__ or __name__)
 
-from embedchain.apps.app import App  # noqa: F401
+from embedchain.app import App  # noqa: F401
 from embedchain.client import Client  # noqa: F401
 from embedchain.pipeline import Pipeline  # noqa: F401
-from embedchain.vectordb.chroma import ChromaDB  # noqa: F401
 
 # Setup the user directory if doesn't exist already
 Client.setup_dir()