Added custom keywords paramters to the VA's subscribe method.
Merge branch 'master' into development
gui: Legend for spectrogram plotting fix
tiff: change way spectrum is recorded

As proposed on the OME-devel mailing list.
Format is:
 * use Channel.EmmissionWavelength for each spectrum channel
 * record it as float, to keep a good precision
 * set/expect AcquisitionMode "SpectralImaging"
hdf5: fix computation of WL_LIST
fix raise exception with multiple arguments

due to confusion with logging, which accepts multiple arguments, we got a lot of Exceptions while creating exceptions.

Was not terribly bad as the code was unlikely to be called, and would still create an exception. But now we give the right error message.