Add promise support on filters

[gabskoro]

Sometimes you need to do something more in your filter function (will send you another PR for that) and because of that, it would be better to have the isValid method wrapped in a Promise.

There si one catch, cause of the variable this._failFilterIndex we need to resolve each time, so for the users who will use promises they always need to resolve, either with true or false.

[codecov-io]

Codecov Report

Merging #648 into development will increase coverage by 17.27%.
The diff coverage is 27.27%.

@@               Coverage Diff                @@
##           development     #648       +/-   ##
================================================
+ Coverage        33.08%   50.36%   +17.27%     
================================================
  Files               10       10               
  Lines              547      554        +7     
  Branches            70       75        +5     
================================================
+ Hits               181      279       +98     
+ Misses             363      274       -89     
+ Partials             3        1        -2

Impacted Files	Coverage Δ
src/file-upload/file-uploader.class.ts	39.7% <27.27%> (+14.51%)	⬆️
src/file-upload/file-item.class.ts	27.27% <0%> (+5.05%)	⬆️
scripts/matchers.ts	57.14% <0%> (+14.28%)	⬆️
src/file-upload/file-like-object.class.ts	47.36% <0%> (+15.78%)	⬆️
src/file-upload/file-type.class.ts	53.84% <0%> (+30.76%)	⬆️
src/file-upload/file-select.directive.ts	95.45% <0%> (+40.9%)	⬆️
src/file-upload/file-drop.directive.ts	87.03% <0%> (+49.3%)	⬆️

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