Introduce AbstractProvider

[snuyanzin]

There are 2 issues:

1. currently to create and use your own provider it is required to create a custom faker
2. each time a new provider should contain a faker (minor issue but annoying)

The PR introduces an AbstractProvider and makes use it by all providers. Also it allows to create and use custom providers without creation custom fakers, for more details have a look at net.datafaker.CustomFakerTest#insectBeeTestExpressionFromFileWithoutExtraFaker

[codecov-commenter]

Codecov Report

Merging #262 (89743e7) into master (ff9bf48) will decrease coverage by 0.35%.
The diff coverage is 99.66%.

@@             Coverage Diff              @@
##             master     #262      +/-   ##
============================================
- Coverage     94.69%   94.33%   -0.36%     
- Complexity     1888     1889       +1     
============================================
  Files           193      194       +1     
  Lines          3955     3795     -160     
  Branches        393      393              
============================================
- Hits           3745     3580     -165     
- Misses          110      114       +4     
- Partials        100      101       +1     

Impacted Files	Coverage Δ
...main/java/net/datafaker/idnumbers/PeselNumber.java	100.00% <ø> (ø)
...ava/net/datafaker/HitchhikersGuideToTheGalaxy.java	88.88% <87.50%> (-1.12%)	⬇️
src/main/java/net/datafaker/Address.java	94.28% <95.65%> (-0.16%)	⬇️
src/main/java/net/datafaker/AbstractProvider.java	100.00% <100.00%> (ø)
src/main/java/net/datafaker/Ancient.java	100.00% <100.00%> (ø)
src/main/java/net/datafaker/Animal.java	100.00% <100.00%> (ø)
src/main/java/net/datafaker/App.java	100.00% <100.00%> (ø)
src/main/java/net/datafaker/Appliance.java	100.00% <100.00%> (ø)
...c/main/java/net/datafaker/AquaTeenHungerForce.java	100.00% <100.00%> (ø)
src/main/java/net/datafaker/Artist.java	100.00% <100.00%> (ø)
... and 327 more

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