[MOB-2344] Remove PowerMock

[vbabenkoru]

🔹 Jira Ticket(s) if any

• MOB-2344

✏️ Description

There was one test still using PowerMock. This PR refactors IterableActionRunner a bit to make it testable without PowerMock, and removes PowerMock dependency from our project.

[codecov]

Codecov Report

Merging #320 (438c35f) into master (dad4663) will increase coverage by 0.10%.
The diff coverage is 53.12%.

@@            Coverage Diff             @@
##           master     #320      +/-   ##
==========================================
+ Coverage   70.36%   70.46%   +0.10%     
==========================================
  Files          60       60              
  Lines        3698     3701       +3     
  Branches      427      430       +3     
==========================================
+ Hits         2602     2608       +6     
+ Misses        830      829       -1     
+ Partials      266      264       -2     

Impacted Files	Coverage Δ
...com/iterable/iterableapi/IterableActionRunner.java	51.51% <53.12%> (+8.18%)	⬆️
.../iterable/iterableapi/IterableActivityMonitor.java	93.44% <0.00%> (+1.63%)	⬆️
...java/com/iterable/iterableapi/ui/BitmapLoader.java	64.28% <0.00%> (+2.38%)	⬆️

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