1) bug fix: in createDIDL sometimes comes single item, not array. But array is expected. And method crashes.
Fix: detect if single item is come and convert it to array

2) fix bug with "<?xml..." parse error when php option - short tags - is set

3) upnp broadcast sending page
added button for automatically periodical page refresh for sending broadcast packets without cron, for development purposes

4) Plugins class optimization, method get_plugins
make static cache for optimization when multiple call
Merge branch 'develop' of https://github.com/SeregaPru/ampache into SeregaPru-develop
Merge branch 'SeregaPru-develop' into develop