Switch from 'embedding' to 'starting' IPython

Embedding IPython results in issues where import statements and other
globals changes in the shell environment don't work as expected.[1]
As an example, the following commands result in a NameError:

In [1]: import time

In [2]: def foo():
   ...:     print(time.time())
   ...:

In [3]: foo()
---------------------------------------------------------------------------
NameError                                 Traceback (most recent call last)
<ipython-input-3-c19b6d9633cf> in <module>
----> 1 foo()

<ipython-input-2-a038e7f91c93> in foo()
      1 def foo():
----> 2     print(time.time())
      3

NameError: name 'time' is not defined

By switching to use "start_ipython()" instead, we get an environment
more similar to what we get by running `ipython` directly.

[1] ipython/ipython#62

baseplate/server/__init__.py

@@ -374,11 +374,8 @@ def load_and_run_shell() -> None:
 
     try:
         # try to use IPython if possible
-        from IPython.terminal.embed import InteractiveShellEmbed
-        from IPython.core.interactiveshell import DummyMod
-
-        shell = InteractiveShellEmbed(banner2=banner)
-        shell(local_ns=env, module=DummyMod())
+        from IPython import start_ipython
+        start_ipython(argv=[], user_ns=env)
     except ImportError:
         import code