Move all imports to top of file

A few months ago I had an issue setting up mocking because I was
trying to be clever importing these libraries only when I needed
them rather than at the global scope. Someone pointed out to me
that if the imports are at the top of the file Falcon will load
them once when the WSGI server starts, whereas if they are in the
on_get() or on_post() they will load for every request! Also, it
seems that PEP8 recommends keeping imports at the top of the file
anyways, so I will just do that.

Imports sorted with isort.

See: https://www.python.org/dev/peps/pep-0008/#imports

dspace_statistics_api/app.py

@@ -1,4 +1,5 @@
 import falcon
+import psycopg2.extras
 
 from .database import DatabaseManager
 from .items import get_downloads, get_views
@@ -120,8 +121,6 @@ class ItemResource:
     def on_get(self, req, resp, item_id):
         """Handles GET requests"""
 
-        import psycopg2.extras
-
         # Adapt Python’s uuid.UUID type to PostgreSQL’s uuid
         # See: https://www.psycopg.org/docs/extras.html
         psycopg2.extras.register_uuid()