Always mark 'bower_components' folder resource as 'Derived'

Need to always mark the folder that is used by bower to download the dependencies specified in bower.json as 'Derived' in eclipse (call IResource.setDerived(true) on that folder).

Note that the name of 'bower_components' folder may be regulated from .bowerrc file content, so the tooling should mark the correct folder as Derived according to the settings in .bowerrc file (if any).

Derived resources means they were generated automatically, and user changes will be lost on next build. Also, the Derived-flag is to allow JSDT parser/validator to skip these resources if required.