initialize plugins before the formatters

[live627]

Plugins should be initialized before the formatters since they may wish to add or change formatting handlers and since the bbcode format caches its handlers, such changes must be done first.

One possible caveat is that the public API sceditor.command won't work as intended in plugin init—#686 works around this by duplicating some code

	base.commands = utils
		.extend(true, {}, (userOptions.commands || defaultCommands));

That workaround seems kinda ugly to me, and will probably cause some undesired conflicts when running multiple editor instances on the same page. I haven't tested that, though.

Come to think of it, sceditor.formats.bbcode may also exhibit the same behavior due to what looks like shared memory access. I have not tested this either.

I see more of what could lead to surprising results: methods that get pointers to iframe related objects return null, range helper also is null, but those can easily be worked around by waiting for the ready signal.