Add basic syncing to firebase where the local device is the source of truth.

[miguelandres]

-Each device gets its own object in firebase so devices are isolated and there is no cross-device syncing. -The root object for each device is “remixer/” -DEVICE_REMOTE_ID is the first 8 digits of a randomly generated UUID (not personally identifiable). -DEVICE_REMOTE_ID is persisted across application restarts until data is cleared. That will allow to reuse the same URL across different runs targeting the same app/device combination. -Deserialization is done manually, because type erasure in Java makes it near impossible to deal with types. This way the remixer type system remains extensible.

[codecov-io]

Current coverage is 60.28% (diff: 3.61%)

Merging #118 into develop will decrease coverage by 4.46%

@@            develop       #118   diff @@
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  Files            52         53     +1   
  Lines          1322       1425   +103   
  Methods           0          0          
  Messages          0          0          
  Branches        154        171    +17   
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+ Hits            856        859     +3   
- Misses          410        510   +100   
  Partials         56         56          

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