PDA newscast reception

One can one access and view newsfeeds from the comfort of one's PDA.

* Possible to change and disable the newsmessage beep.
* PDAs are only notified about news if they have reception.
* PDAs can only fetch new feeds and their messages if they have reception.

Known issues:
Unlike browse() NanoUI does not appear to wait for browse_rsc(), the method which to transfers image to the client's cache, to finish.
This often results in newsfeeds not always displaying their images the first time they are viewed.