Misc search touch ups and general clean up

[GustavoSanMartin]

Checklist

• [x] I ran ./gradlew test connectedAndroidTest detekt
• [x] I rebased off of upstream/master
• [ ] ~I added tests if applicable~

Summary

Search

• Added back button.
• Made scrim clickable.
• Added selectable background to search results.

  Other

• Reorganized xml layout files.
• Removed unused files.
• Replaced foregrounds with backgrounds.

[codecov[bot]]

Codecov Report

Merging #78 into master will decrease coverage by 0.48%. The diff coverage is 0%.

@@            Coverage Diff             @@
##           master      #78      +/-   ##
==========================================
- Coverage   30.01%   29.52%   -0.49%     
==========================================
  Files          70       70              
  Lines         973      989      +16     
  Branches      141      142       +1     
==========================================
  Hits          292      292              
- Misses        625      641      +16     
  Partials       56       56

Impacted Files	Coverage Δ
.../ca/llamabagel/transpo/search/ui/SearchActivity.kt	0% <0%> (ø)	:arrow_up:
.../search/ui/viewholders/SearchCategoryViewHolder.kt	0% <0%> (ø)	:arrow_up:
...a/ca/llamabagel/transpo/search/ui/SearchAdapter.kt	0% <0%> (ø)	:arrow_up:

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