Simplify and improve 'list' property

When a source/output/etc has a property of a 'list' type, there was no
way to get the names associated with its values.  That, and it only
supported lists of either text, or enums (0..[value] only).

Now, you can associate translated names with those values, and use
integer, float, or string values.  Put it all in to one function as well
to simplify its usage.

I plan on using this to help get enumerations from devices/etc for
certain types of sources.  For example, if I get the properties of an
audio source, I'd like to have a list of available devices with it as
well.