WIP: Add new submission class which will communicate with the RWTH JupyterHub service

/cc @rohlfing

examples/submission.ipynb

+%% Cell type:markdown id: tags:
 
+# Example notebooks for using the submission service
 
+%% Cell type:code id: tags:
 
+``` python
+from rwth_nb.misc.submission import Submission
+
+from random import randint
+from pprint import pprint
+
+sub = Submission('test_realm')
 ```
 
+%% Cell type:code id: tags:
 
+``` python
+print('\nCreate some random submissions...')
+for i in range(5):
+    sub.submit({
+        'random_integer': randint(1, 100)
+    })
 ```
 
+%% Cell type:markdown id: tags:
 
+## Admin actions
+
+For performing admin actions the user must own the role manager-{profile_slug} or submission-{realm}
 
+%% Cell type:code id: tags:
 
+``` python
+print('\nAll submissions:')
+pprint(sub.get_all())
+
+print('\nDelete all submissions')
+sub.delete_all()
+
+print('\nAll submissions:')
+pprint(sub.get_all())
 ```
 
+%% Cell type:markdown id: tags:
 
+## User actions
 
+%% Cell type:code id: tags:
 
+``` python
+if sub.is_submitted():
+    print('\nEvaluation already submitted')
+else:
+    print('\nNothing submitted yet!')
+    sub.submit({'test': [1, 2, 3]})
+
+    if sub.is_submitted():
+        print('\nNow it is submitted!:')
+        pprint(sub.get())
+
+print('\nMy submissions:')
+mysubs = sub.get()
+print(mysubs)
+
+ident = mysubs[0]['id']
+print(f'\nMy submission ID: {ident}')
+
+print(f'\nDeleting my submission with ID: {ident}')
+sub.delete(ident=ident)
+
+print('\nMy submissions:')
+mysubs = sub.get()
+print(mysubs)
 ```
 
+%% Cell type:markdown id: tags:
 
+## Submitting whole notebooks
+
+The following cell submits the current notebook contents
 
+%% Cell type:code id: tags:
 
+``` python
+sub.submit_notebook()
 ```
 
+%% Cell type:markdown id: tags:
 
+The following cell fetches all submitted notebooks in the current realm by the current user and stores them in the current directory
 
+%% Cell type:code id: tags:
 
+``` python
+sub.fetch_notebook(subdir='fetched_notebooks', prefix='a1')
 ```