Feature/#204 consolidate search and multiselect

[iguannalin]

See issue: #204

[iguannalin]

We may want to look into possible performance enhancements to avoid visual latency in that part of the application.

I should note that performance is always slightly better in the actual live deployment (presumably because of optimizations in the production build), so we may want to do more testing of the performance just in case I'm wrong in my method of measurement. Probably the best way to test performance is to check out the previous version (4.3) and run it in parallel on a different port and take the average of 10 observances of mousenter or something to that effect. This will produce closer conditions than in my testing.

@isaisabel, I looked into this and tested the performance of the mouseenter event in 4 environments:

1. locally, develop branch (65.78ms)
2. locally, master branch (78.78ms)
3. locally, feature/# 204 branch (76.59ms)
4. deployed v4.3 (20.08ms)

I tested this by running the performance profiling, reloading the page, and hovering over the 4 techniques in the top left corner after the matrix loads. It seems to take consistently ~60-80ms for the mouseenter event when running locally (I ran these about 2-3 times), and significantly less at 20ms in the deployed version on the mitre-attack site.

If I'm doing this right and understanding you correctly, I'm not sure if there's a significant lag in the mouseenter/hover because of the changes in this feature branch. One thing I do think concerns me about performance when working on this feature though, was the loading of all the techniques in the search component sidebar (since it now loads & searches techniques across domains and all techniques).

Screenshots:

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[isaisabel]

I actually have found one major bug in my second review. When switching between layers of different domains, the contents of the sidebar does not update properly until a query is added.

Steps to reproduce:

1. Open two layers, one Enterprise and one Mobile
2. Open the sidebar on both tabs
3. Switch back and forth between the two tabs. The counts and listed objects should change when switching tabs since the data under each domain is different, but this does not happen. Only when a query is inputted do the objects listed refresh.

Aside from that everything looks great, and the added denounce definitely makes the search input more performant.

[isaisabel]

Looks great! I pushed a commit which updates the help page documentation which was pretty old for this feature (it didn't mention mitigations which were not originally part of the interface and generally needed a touch-up).