rename registered? to announced?
introduce activated? and adapt registered? method
add product_activated? and system_activated? methods to the YAST wrapper class
remove system_activated? method from YaST wrapper class
get rid of registered?
rename activated? to activated_base_product?
rename announced? to credentials?
Merge pull request #126 from SUSE/review_140630_extend_yast_wrapper_to_include_activated_

[Review] Request from 'vlewin' @ 'SUSE/connect/review_140630_extend_yast_wrapper_to_include_activated_'