Add Javadoc autogeneration that works on Jitpack

[miguelandres]

Generates javadoc that includes the whole scope of remixer_core, remixer_annotation, remixer_ui and remixer_storage, merging all of them into one source set.

Hacks had to be made to accommodate the fact that some are java libraries and some are android libraries.

Added a link to the develop branch snapshot's javadoc to the Readme. this link won't work until this diff is merged but you can preview it on the javadoc branch snapshot.

Fixes #60

[chuga]

👏

[codecov-io]

Current coverage is 68.96% (diff: 100%)

Merging #109 into develop will not change coverage

@@            develop       #109   diff @@
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  Files            49         49          
  Lines          1247       1247          
  Methods           0          0          
  Messages          0          0          
  Branches        146        146          
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  Hits            860        860          
  Misses          335        335          
  Partials         52         52          

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