Adds "exec" command and other BotManager tweaks.

Allows commands to be given directly to bots via the BotManager
console.This command is handled in the UserHandler's `OnBotCommand`.

Other changes include threading the BotManager commands and
slightlychanging the way accounts are authorized while
`UseSeparateProcesses  = true`.

Extended functionality of the "start", "stop", and "auth" commands to
allow usernames as well as indexes.

Also fixed the `Console.Title` being set to the last bot to be
configured while in Separate Processes mode.
Removes command threading. Username comparisons changed to ignore case.

As per suggestions, the bot command is no longer threaded, and a couple
conditionals are inverted. This also modifies username comparisons which
now use `StringComparison.CurrentCultureIgnoreCase`.