Screen Orientation plugin - add support for browser platform

Based on Pull Request #110

from FuzzyRhombus:

Some browsers can lock/unlock orientation when in fullscreen mode only - this simple change allows your API to still work in browsers as long as the needed functions are available and an element is currently fullscreen. I'd like to be able to handle this case without having to go around the plugin API and I don't see why anyone would object to having the option.

See original PR for additional discussion and reference code.