Arctic Icon Request Versions Save

1. Fixed various bugs, especially around Arctic Manager interaction.
2. Updated internal dependencies and target SDK.
3. Improved error handling.

1. Fix how Retrofit is used.
2. Process response body with remote requests to verify we are receiving "success" from the API.
3. Add some logging.

Thanks to @jahirfiquitiva for noticing an error in the code.

Update the User-Agent header.

performSend and performLoad have an optional callback lambda now, in addition to the callbacks that can be set in the ArcticRequest constructor.

Checkout the README.

This is basically a re-write of the library.

1. Everything is now written in Kotlin.
2. RxJava is no longer exposed to library consumers, it's only used internally.
3. The whole API should now feel simpler to use.

See the README for usage.

Migrated to RxJava 2