BridgeAbstract will return 3600 seconds by default, so the function
can be removed from any bridge implementing getCacheDuration
returning the same value.
Documentation updated accordingly.
Many bridges implemented getDescription() which is only applicable for
bridges extending RSSExpander.
Functions that are not part of the abstract class or interface should
be in private scope for better readability.
Images from their own servers are linked relatively via 'local/...' we
must replace this for images to point to the correct destination.
Also use strip_tags to get rid of iframes
This fixes error "Using $this when not in object context"
Nested functions are not part of the object and therefore don't have
access to the object instance $this!
