all: Update source-tags for all plugins

Add relevant tags for most plugins, including "net:internet" for a large
number of plugins that wouldn't be usable without an Internet
connection.

Note that a number of plugins were not marked as "net:internet" despite
requiring an Internet connection to fetch new data because they do have
local caching support (thetvdb and pocket for example).

Plugins that use data from the local network but use other discovery
methods (Freebox and DAAP with mDNS, Dleyna with DLNA/UPnP) were also
not marked, as they will disappear if the shares become unavailable.

https://bugzilla.gnome.org/show_bug.cgi?id=725148