plugout tidy up

[kjdon]

Tidy up plugouts in same way we have done plugins. PrintInfo would be almost exactly the same as plugin one - use the same class??

export.pl has lots of options that are specific to each plugout. remove them from the script, and make plugouts specified in collect.cfg so options are passed in in the same way that plugin options are.

import saveas thing should also use plugout options from config file

see also #332.

[kjdon]

oh, you can export several collections at once. Where should plugout info go? a new export.cfg file?

[kjdon]

I am just removing the facility to export more than one collection at once, cos its thought that no one would ever want to do it.

so plugout options can go into the config file.