Added SchemaPayload

- Made changes to Tracker to support this
- Untested, so this is still volatile
Moved Payload classes to emitter module
More changes to support SchemaPayload
Fixed version with prepending java
Removed additional timestamp addition in payload
Fixed exponential in timestamp
Bug in POST payload

Sets data to an array of maps instead of Payload
In-line documentation for Payload
In-line documentation for Tracker
In-line documentation for Emitter
Fix bug with context needing to be list of maps

- Fixes #56
Fixes a bug with the schema version
Empty commit to close issues

- Fixes #50
Fixed Tracker test
Moved root project to java-tracker-core

- Fixes #47
Fixed build.gradle for java-core project
Removed unnecessary imports
Added gradle-wrapper.java back again
Fixed changelog rename & updated