Add a new paused attribute to the carousel

[ghinda]

Add a new paused attribute to the carousel, that allows you to pause the carousel, without having to change the interval value.

This is more convenient, rather than having to keep old/new values for the interval, when changing it to a negative value.

I've also change the demo to be able to test the new attribute.

[pkozlowski-opensource]

@cristiancolceriu are you trying to control carousel from "outside" of it? What is your use case? I don't mind merging it, just trying to understand the context. @ajoslin WDYT?

@cristiancolceriu one more thing - we will need tests for this change as well.

[ajoslin]

I guess paused attribute is cool to have - I like it. Once you add unit tests I'm OK with merging it.

Although, we will have to set it the other way too. When scope.pause() is called inside the carousel, it should set scope.paused. Same with scope.play(). Will definitely need some unit tests :)

[ghinda]

Yes, exactly. I'm trying to control the play/paused state from outside the carousel.
Will push one or more unit tests in a couple of days.

Sorry about the username mix-up. I've committed the code from a different location and Github seems to have picked up my other username. @ghinda is my main account.

[pkozlowski-opensource]

@ghinda Haven't heard from you for a while and as noted, this PR needs some more work before it can be merged. Most notably tests are missing. Trying to clean up the PRs queue a bit so going to close this one for now. Please open another PR when you've got time and tests ready.