Added multiple file selection (very basic form) to conversion wizard.
This adds a lot of confusion to the GUI however has been requested from
the powers that be. It does not fully work as yet and requires more
testing and polishing. The ascii conversion does not support multiple
files as yet either but can do in the same way that the AVI conversion
was made to support it.
Merge branch 'master' of git@github.com:DawnScience/dawn-common.git