Handle command errors and ctrl+d commands in UI

CHANGELOG.md

@@ -2,6 +2,7 @@
 
 ## Latest
 
+- [Improvement] Error and interrupt handling in UI and web UI
 - [Bugfix] Fix missing webui env directory
 
 ## 3.1.0 (2019-03-09)

tutor/ui.py

@@ -9,5 +9,10 @@ def ui():
     click.echo("""Welcome to the Tutor interactive shell UI!
 Type "help" to view all available commands.
 Type "local quickstart" to configure and launch a new platform from scratch.
-""")
-    click_repl.repl(click.get_current_context())
+Type <ctrl-d> to exit.""")
+    while True:
+        try:
+            click_repl.repl(click.get_current_context())
+            return  # this happens on a ctrl+d
+        except Exception:
+            pass