Prevent additional possible crash(es) from improperly disposed observables.

[dbrant]

You've got some additional helper classes that perform Rx operations internally on their own. These, too, need to be contained and disposed when they are no longer needed (i.e. no longer associated with an activity or fragment).

[codecov-io]

Codecov Report

Merging #2670 into master will increase coverage by 0.05%.
The diff coverage is 47.61%.

@@            Coverage Diff            @@
##           master   #2670      +/-   ##
=========================================
+ Coverage    2.76%   2.82%   +0.05%     
=========================================
  Files         259     259              
  Lines       12367   12375       +8     
  Branches     1112    1112              
=========================================
+ Hits          342     349       +7     
- Misses      11998   12000       +2     
+ Partials       27      26       -1

Impacted Files	Coverage Δ
...ree/nrw/commons/upload/ImageProcessingService.java	84.48% <100%> (ø)	⬆️
...java/fr/free/nrw/commons/upload/FileProcessor.java	5.33% <25%> (+1.16%)	⬆️
...va/fr/free/nrw/commons/upload/UploadPresenter.java	11.04% <28.57%> (+0.37%)	⬆️
...n/java/fr/free/nrw/commons/upload/UploadModel.java	34.25% <62.5%> (+2.41%)	⬆️

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[dbrant]

Consolidated into #2669