Better attachment action features

[maknz]

We've got the base for attachment actions in master (yet unreleased) thanks to @janek2012. I'd like to go further and allow for developers to easily respond to actions when called back by Slack.

I'd also like to simplify the class names (including the existing ones) so things are more fluid. Action rather than AttachmentAction for example.

[luckygulli]

I get an error due to this line : 'confirm' => $this->getConfirm()->toArray(),

Call to a member function toArray() on a non-object

So I must at least add 'confirm' => [] to avoid the error (but It show a confirmation Dialog...)

I think we must be able to setConfirm to null (to delete confirmation Dialog) and handle without confirm. :)

I will not have the time to test it as I should do, so I prefer let you do it.

Thank you! :)
PS : Great Job !

[youuri]

Hey, still in progress? Need some help maybe?