Jupyter messaging updates/correctness

[halleysfifthinc]

• Bump Julia compat to be able to use pkgversion in "kernel_info_request" to report the IJulia version
• Some messages and responses were sent on the wrong channel:
  • Replies should be sent to the channel the request was sent on
    • This is not 💯 explicit in the messaging protocol docs, but appears to be the norm. Some messages are only described as always being sent (by the frontend/client) on a specific channel, but e.g. I saw "kernel_info_request" sent on both the shell/requests channel AND the control channel. (The latter is not described as possible according to the docs.)
• Replies should always have a { 'status': 'ok' }
• The transient metadata field was added in protocol version 5.1. Without the ability to add transient metadata, "update_display_data" messages can't be used to update/redisplay existing outputs (while participating in/with the rest of the IJulia display machinery). Related PR Function to publish raw/encoded display data #946 is more extensive and stalled; this is the minimum necessary change to support this.

Fixes #953
Fixes #1000

Reference: https://jupyter-client.readthedocs.io/en/latest/messaging.html

[halleysfifthinc]

Bump

[JamesWrigley]

Not strictly necessary for this PR, but we should start using jupyter_kernel_test in the tests: https://github.com/jupyter/jupyter_kernel_test

[codecov]

Codecov Report

Attention: Patch coverage is 0% with 6 lines in your changes missing coverage. Please review.

Project coverage is 10.48%. Comparing base (2164bfc) to head (57df15d).
Report is 8 commits behind head on master.

Files with missing lines	Patch %	Lines
src/handlers.jl	0.00%	3 Missing ⚠️
src/IJulia.jl	0.00%	1 Missing ⚠️
src/comm_manager.jl	0.00%	1 Missing ⚠️
src/display.jl	0.00%	1 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##           master    #1138      +/-   ##
==========================================
- Coverage   10.51%   10.48%   -0.03%     
==========================================
  Files          14       14              
  Lines         818      820       +2     
==========================================
  Hits           86       86              
- Misses        732      734       +2     

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[JamesWrigley]

LGTM!