Update ReplyAsync Task to return the sent message.

This property previously had a default value of 'null'. In DiscordSocketClient#ConnectInternalAsync, we would attempt to send a null status to Discord, which would fail to serialize, and force the client to disconnect.

Adjusted GetGuildPruneCount to using params;

fixes #240

Fix #323

thanks to auxesis for the find

Moved IDeletable interface up inheritance to IMessage

Fix #320

I'm not entirely sure this is the proper way to fix this. However, it seems like
SendFileAsync returns the Task<RestUserMessage>, which would exit the using
block, disposing of the FileStream potentially before the Task is finished.

Changed to await the result of the task before exiting the using block.

Move DI stuff around to support scoped DI

Prevents an NRE when creating a CommandContext from a message in an IDMChannel

Fix #311

TypeInfo.BaseType will likely return the same Type if all modules derive from
ModuleBase or some common subclass of it. Making it appear as if only one module
is registered.

Changed to TypeInfo.AsType for expected behavior.

this one took a while

Exclude abstract types from being loaded as modules.