Fix nullref during CreateRoleAsync

Access "Date" in response header safely with TryGetValue. Hopefully nothing bad happens when lag is 0

In cases where Discord sent a value of `id=0`, this would throw an invalid-cast, where 0u64 cannot be cast to string.

this is all really broken

Property can be renamed as needed.

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