Prevent mutation menu closing when clicking on another task or cycle

[MetRonnie]

These changes close #916

Requirements check-list

• I have read CONTRIBUTING.md and added my name as a Code Contributor.
• Contains logically grouped changes (else tidy your branch by rebase).
• Does not contain off-topic changes (use other PRs for other changes).
• Appropriate tests are included (e2e).
• Appropriate change log entry included in Prepare release: 1.0.0 #935
• No documentation update required.

[codecov]

Codecov Report

Merging #927 (73958fb) into master (af4ae02) will increase coverage by 0.27%.
The diff coverage is 100.00%.

@@            Coverage Diff             @@
##           master     #927      +/-   ##
==========================================
+ Coverage   90.30%   90.57%   +0.27%     
==========================================
  Files          92       92              
  Lines        2000     2005       +5     
  Branches      151      152       +1     
==========================================
+ Hits         1806     1816      +10     
+ Misses        168      163       -5     
  Partials       26       26              

Flag	Coverage Δ
e2e	76.90% <100.00%> (+0.45%)	⬆️
unittests	78.25% <100.00%> (ø)

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Impacted Files	Coverage Δ
src/components/cylc/cylcObject/Menu.vue	77.77% <100.00%> (+1.91%)	⬆️
src/components/cylc/cylcObject/plugin.js	100.00% <100.00%> (ø)
src/utils/aotf.js	95.93% <0.00%> (+2.53%)	⬆️

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[MetRonnie]

I think this was a mistake, the first arg should be the event that you're removing the listener for

[AaronDCole]

Seems to work as expected!

[hjoliver]

Looks sensible, and works for me too.

I'll leave it for @wxtim to merge (sounds like he wants to look at the code more closely) [Oops wrong PR for that statement!]