Prepare discord-rpc 1.5

[DeJayDev]

All changes:

• Uses HTML in README.MD to right align discord-rpc logo
• Fixes typo in README.MD
• Converts the RPCTest project to a fully Maven based project
• Rewrite the RPCTest project's main file in an attempt to fix various bugs found in dev
• Moves ReadyCallback to a new class file
• Updates commons-io to 2.6
• Updates discord-rpc-binaries to 3.3.0
• Updates maven-shade-plugin to 3.1.1
• Updates maven-compiler-plugin to 3.7.0
• Rewrite OS check in discord-rpc.jar to use home based dirs instead of System Properties
• Fixes various spacing problems
• Changes version of discord-rpc.jar project to 1.5.0