[PD] translation support for search plugin

[Hans-Christoph Steiner]

Hey Jonathan,

It would be very nice for people to be able to translate the Search Plugin
into whatever language they want.  Mostly that means surrounding every string
with [_ ], then the translation tools to the rest.  There are some strings in
the current plugin that are setup this way, but most are not.

Ideally, plugins would be able to include their own translations.  That means
adding support to Pd-extended, which I can do.

.hc