#18 Support for user-defined Metadata on all types

[Henrique de Moraes Holschuh]

With a small bit of tweaking, it should be possible for
IPplan to greatly improve its support for
characteristics of an IP, subnet, supernet/range or area.

Take the current aproach for searching "free" subnets.
It is not internationalized, and it is a pain to so. It
is based on a hardcoded string search. It doesn't
allow the user to add aditional data (otherwise the
string changes, and the "locate free" function won't
match).

An alternative approach would be to add for each object
a field where one can add tags, and some of tags can be
made pointers to generic text.

"Free" would be one of the builtin tags, then (and a
boolean one). A non-boolean generic tag could be
something like foo:<number>, which translates to text
data in table metadata_foo, id (primary key) <number>.

A tag's title, label, etc would be in another table
(say, metadata, with columns id (the "foo" above),
label (whatever appears in the interface near an
dropbox/inputbox), help text, type (boolean, text), etc.)

A tag not present in the taglist for an object would be
considered empty(text, same as N/A) or false(boolean tags).