Allow overwrite existing uploads

[lhalaa]

Resolves #21

[codecov]

Codecov Report

Merging #30 into master will increase coverage by 5.25%.
The diff coverage is 89.47%.

@@             Coverage Diff              @@
##             master      #30      +/-   ##
============================================
+ Coverage     90.65%   95.91%   +5.25%     
- Complexity      118      123       +5     
============================================
  Files            12       12              
  Lines           396      416      +20     
============================================
+ Hits            359      399      +40     
+ Misses           37       17      -20

Impacted Files	Coverage Δ	Complexity Δ
src/models/PartialFormSubmission.php	96.92% <100%> (+0.2%)	16 <1> (+1)	⬆️
src/controllers/PartialSubmissionController.php	95.71% <87.5%> (-1.35%)	23 <4> (ø)
src/controllers/PartialUserFormController.php	88% <88.46%> (+60.22%)	15 <3> (+4)	⬆️
src/models/PartialFileFieldSubmission.php	85.71% <0%> (+7.14%)	7% <0%> (ø)	⬇️

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[Firesphere]

Could you add some tests? It's better to keep the testing quality up than letting it go

[lhalaa]

Could you add some tests? It's better to keep the testing quality up than letting it go

I won't have time to add all the tests, so my tests will be limited

[lhalaa]

Moved to #32