Refactor ShareActivity

[misaochan]

Fixes #1091 . Tested by uploading via app and "share" on prodDebug build, real device running Android 7.0.

Changes made:

• Directed all upload entry points to ShareActivity. MultipleShareActivity.java will be removed completely in a future PR This redirection cannot be done yet if we are to release 2.8 with this PR.
• Added Javadocs to methods of ShareActivity
• Reduced number of lines in ShareActivity from 1000+ to 600+ by extracting file processing functions to FileProcessor.java (if they made sense to be associated with an object) or to FileUtils.java (if they made sense to be static), and extracting zoom functions to Zoom.java.
• Unified the FileUtils in Upload package and the FileUtils in Utils package, as there is no point in having 2 different FileUtils and it was causing a lot of confusion
• Simplified permission logic in ShareActivity, there is no point having storage permissions requested in the snackbar as well as at the Submit button, as it is mandatory. The snackbar is now used solely for the optional Location permission
• Removed as much unnecessary code as possible from onCreate(), reducing number of lines by more than half

[codecov-io]

Codecov Report

Merging #1552 into master will increase coverage by 0.01%.
The diff coverage is 0%.

@@            Coverage Diff            @@
##           master   #1552      +/-   ##
=========================================
+ Coverage    3.86%   3.87%   +0.01%     
=========================================
  Files         149     150       +1     
  Lines        7576    7556      -20     
  Branches      721     708      -13     
=========================================
  Hits          293     293              
+ Misses       7266    7246      -20     
  Partials       17      17

Impacted Files	Coverage Δ
...n/java/fr/free/nrw/commons/CommonsApplication.java	30.61% <ø> (ø)	⬆️
.../java/fr/free/nrw/commons/nearby/NearbyPlaces.java	0% <ø> (ø)	⬆️
...free/nrw/commons/upload/MultipleShareActivity.java	0% <ø> (ø)	⬆️
...fr/free/nrw/commons/settings/SettingsFragment.java	30% <ø> (ø)	⬆️
...ain/java/fr/free/nrw/commons/upload/FileUtils.java	3.22% <0%> (-2.53%)	⬇️
...java/fr/free/nrw/commons/upload/FileProcessor.java	0% <0%> (ø)
...java/fr/free/nrw/commons/upload/ShareActivity.java	0% <0%> (ø)	⬆️
...src/main/java/fr/free/nrw/commons/upload/Zoom.java	0% <0%> (ø)

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[misaochan]

@maskaravivek @neslihanturan This is now ready for review. :) I believe it will make fixing #1485 easier after this is merged, as ShareActivity will be more manageable.

[maskaravivek]

Tested both Nearby uploads and normal upload flow. It works perfectly. Thanks, @misaochan for taking up the refactoring. :)