[TxMt Plugins] Dialog API improvements

[Rob Rix]

>> You can do the same thing with a single subcommand name ("tm_dialog
>> create-window file.nib") as a part of the command name by storing a
>> "command -> [class, selector]" mapping instead of the simpler "noun  
>> ->
>> class" mapping. But I think I still prefer the "noun verb" syntax,
> I find it a bit verbose and unfamilar (I do not think I have used many
> shell commands that use
> this structure), but I have no proplems accepting it if it is what  
> people
> want.

e.g. git and svn have fairly verbose syntaxes; the various Rails  
scripts tend to also, although that's a less compelling case.

I'm in favour.

Rob