is there an app that can rotate my home screens when the phone is in landscspe, for example when the phone is used in a holder in landscape but you still want to flick through your apps etc

I used to use this and found it brilliantly effective - https://play.google.com/store/apps/details?id=com.devasque.rotationlocker

does it rotate the home screen too?

That is what you asked for :-P

Just install a different Launcher (Apex, Nova, Go etc...)

 

They all have the ability to 'Auto Rotate' your homescreen a full 360 degrees

 

Plus you can customise your icons and resize widgets etc!

Hope I didn't offend earlier - posted tongue in cheek

lol not at all!