fix(camera-preview): Changes implementation to match Cordova plugin

[amuramoto]

• Changes interfaces to match plugin
• Minor docs updates
• Changes startCamera() function signature to match plugin

[ihadeed]

Thanks Alex

We keep a prefix for the interface name to make sure that there are no conflicts in the future (in case another plugin uses the same name for their interfaces).

[amuramoto]

No problem. I've prefixed the Size and Rect interfaces

[ihadeed]

thanks @amuramoto