PR: Remove IPython kernels from the Python console and connect directly to them

[ccordoba12]

Fixes #1860
Fixes #2696
Fixes #2790
Fixes #2844
Fixes #2846
Fixes #2918
Fixes #2945
Fixes #3011
Fixes #3109

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This is our fourth iteration(!) to integrate qtconsole within Spyder. The first one was created by Pierre in 2.1, and I Improved what he did in 2.2 and again in 2.3.

The idea this time is to avoid creating IPython kernels as widgets in the Python console, and instead talk to them directly. Of course, this is a major undertaking and so I've been procrastinating to do it for a long time! :-)

The advantages of this approach are:

• Remove perhaps the ugliest UX present in Spyder at the moment
• Avoid a ton of intricate code to maintain kernels and IPython consoles in sync
• A promising approach to improve our debugging experience in a future release (4.0?)

Tasks:

• Reestablish connection with the Editor
• Reestablish connection with the Help plugin
• Reestablish connection with the Variable Explorer (this is the hardest task!)
• Remove unneeded code from the Python console

[dhirschfeld]

FYI: On this branch I can't open an IPython console - I get the below error in the internal console:

>>> Traceback (most recent call last):
  File "C:\Users\Dave\Code\spyder\spyderlib\plugins\__init__.py", line 503, in <lambda>
    toggled=lambda checked: self.toggle_view(checked),
  File "C:\Users\Dave\Code\spyder\spyderlib\plugins\ipythonconsole.py", line 689, in toggle_view
    self.create_new_client(give_focus=False)
  File "C:\Users\Dave\Code\spyder\spyderlib\plugins\ipythonconsole.py", line 876, in create_new_client
    self.connect_client_to_kernel(client)
  File "C:\Users\Dave\Code\spyder\spyderlib\plugins\ipythonconsole.py", line 1126, in connect_client_to_kernel
    client.password)
  File "C:\Users\Dave\Code\spyder\spyderlib\plugins\ipythonconsole.py", line 1098, in create_kernel_manager_and_client
    kernel_manager.kernel_spec = self.create_kernel_spec()
AttributeError: can't set attribute

[ccordoba12]

@dhirschfeld, thanks for testing. I'll see what's happening :-)

[ccordoba12]

I think this one is finally ready!! There are some missing things (like inspecting values in the Variable Explorer while debugging) but I'll fix them in 3.1.

For now the most important things are working, i.e. the connections with the Editor, Help and Variable Explorer in normal mode.

[goanpeca]

👍

[ccordoba12]

Perhaps what I did is not the best approach (we could have used comm messages for some parts), but it's working for now ;-)

[goanpeca]

Lets create an issue so we can track these things you suggest we use