[pvr] adds 'Find similar' button to guide info dialog

This adds a new button 'Find similar programs' to the guide info dialog which will trigger a search for similar programs.

I'm not sure if we should add a new language key for the button because the current label is to long and scrolls within the button.

@Jalle19 or @opdenkamp for review the core part
@ronie or @BigNoid for the changes i made to confluence
Can this be null?