Add structures to support hot restarting

[freya022]

Deprecations

• Deprecated BotCommands#create(<configuration block>)
  • Added an overload accepting the arguments of the main method
• Deprecated JDAConfiguration.DevTools
  • Replaced with shutdownTimeout in BConfig, which applies to the entire framework's shutdown

New Features

• Added BContext#shutdown
• Added BContext#shutdownNow
• Added BContext#awaitShutdown
• Added SHUTTING_DOWN and SHUTDOWN in BContext.Status
• Added BConfig#enableShutdownHook
• Added BConfig#shutdownTimeout
• Added BConfig#args
  • Not directly configurable, passed in the entry point or retrieved from Spring
• Added BRestartConfig
• Added BShutdownEvent
• Added ApplicationStartListener
  • Will most likely be only used by the restarter module

Changes

• Made internal coroutine dispatchers use daemon threads
  • So the JVM can exit if the bot is shut down (assuming the user does not create more non-daemon threads)
• Moved RequiresDefaultInjection to the API
• Added isDaemon to namedDefaultScope, defaults to false (compatible)

To do

• [ ] Don't activate outside of development environments
• [ ] Fix trying to access JDA from a closed Spring ApplicationContext on shutdown
• [ ] Have the JDA cache not have a bajillion gotchas
• [ ] Docs
• [ ] Fix resource leaks, if any (threads, classes referencing old restart class loaders)
• [ ] Fix all TODOs