Enhancement: Overhaul logging and implement canonical Logger API

[noahc3]

We currently use Harmony's FileLog API to log debug messages. This has disadvantages:

• Log outputs to file on desktop by default (WTF?)
• Users can turn Harmony debug logging on or off with HARMONY_DEBUG, but this does not affect other plugins using FileLog, these will still output to a file on the desktop (also WTF??)

Let's just sidestep Harmony's weird logger and build our own. Expose a static Logger API from AffinityPluginLoader.Core, make it print pretty messages with timestamps, log levels and source plugin name.