Use smarty3 as default template engine

That's a big one...

From this thread:
https://friendika.openmindspace.org/display/friendicadevelopers/1309670

* 'smarty3' as default template engine ('internal' still here, but must be enabled and all templates must be written)
* removed all 'internal' template files
* templates are loaded from subdir 'templates' (instead of subdir 'smarty3': view/theme/$theme/templates/$name; view/theme/$theme_extended/templates/$name; view/templates/$name
* view/smarty3 is stil used as basedir for smarty cache and work files
* new pluggable template engine system

Other themes will not work until updated (delete old .tpl files, rename smarty3/ to templates/)