Improve advanced multiselect

[mssalvatore]

What does this PR do?

Fixes #891.

Master checkboxes can now have a mixed state.

PR Checklist

• Have you added an explanation of what your changes do and why you'd like to include them?
• Is the TravisCI build passing?
• Was the documentation framework updated to reflect the changes?

Testing Checklist

• Added relevant unit tests? (N/A)
• Have you successfully tested your changes locally? Elaborate:

  Tested by running the Monkey Island locally

• If applicable, add screenshots or log transcripts of the feature working

Testing GIF

Explain Changes

The AdvancedMultiSelect should adhere to some set of human interface guidelines. In the absence of a formal, agreed upon set of guidelines for Infection Monkey, this commit uses KDE's guidelines for checkboxes: https://hig.kde.org/components/editing/checkbox.html

When child checkboxes are not all checked, the master checkbox displays a mixed-state icon, instead of a checked icon. Clicking the mixed-state icon checks all child checkboxes. Clicking an unchecked master checkbox also enables all child checkboxes.

In the past, clicking an unchecked master checkbox checked only the default child checkboxes. While this may seem desirable so that unsafe exploits do not accidentally get selected by the user, it will confuse and frustrate users, as master/child checkboxes do not normally function this way. If there is concern that users may unknowingly select unsafe exploits/options, we should pop up a warning to inform the user when the config is saved/submitted.

[codecov]

Codecov Report

Merging #920 (09a8415) into develop (816c108) will decrease coverage by 41.49%.
The diff coverage is 7.57%.

@@             Coverage Diff              @@
##           develop     #920       +/-   ##
============================================
- Coverage    60.56%   19.07%   -41.50%     
============================================
  Files          166      338      +172     
  Lines         4953    11482     +6529     
============================================
- Hits          3000     2190      -810     
- Misses        1953     9292     +7339     

Impacted Files	Coverage Δ
monkey/common/cloud/azure/azure_instance.py	0.00% <0.00%> (ø)
monkey/common/cloud/gcp/gcp_instance.py	0.00% <0.00%> (ø)
monkey/infection_monkey/exploit/drupal.py	0.00% <0.00%> (ø)
monkey/infection_monkey/exploit/hadoop.py	0.00% <0.00%> (ø)
monkey/infection_monkey/exploit/shellshock.py	0.00% <ø> (ø)
monkey/infection_monkey/exploit/smbexec.py	0.00% <0.00%> (ø)
monkey/infection_monkey/exploit/web_rce.py	0.00% <0.00%> (ø)
monkey/infection_monkey/monkey.py	0.00% <0.00%> (ø)
monkey/infection_monkey/network/network_scanner.py	0.00% <0.00%> (ø)
monkey/infection_monkey/network/tools.py	17.44% <0.00%> (ø)
... and 528 more

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[VakarisZ]

Nice touch of adding mixed state to master checkbox component! Also, did some good refactoring, but there are some things that I don't like/understand.

[mssalvatore]

This PR is getting fairly long and I think it has accomplished it's mission:

1. Resolve issue Plugin selector has wrong inital state. #891
2. Make the master checkbox behavior consistent with a user's expectations
3. More clearly indicate to the user which options are unsafe.

This PR is missing a modal dialog that pops up and warns the user when they import or attempt to submit an unsafe config. #946 has been created to track that feature.

Given that, now, when unsafe options are selected, users have more warning than they did before, I think this PR can proceed without the inclusion of the modal dialog.

[VakarisZ]

Preem quality stuff. But look at my suggestions before merging