acq stream: modify FluoStream .excitation and .emission to reflect hardware capabilities

In order to be able to show in the GUI the hardware settings, we need to express
the emission and excitation directly as the hardware settings.

This avoids the stream to try to be too clever, so that the GUI will be using the util.fluo
functions to try to be clever _and_ warn the user if the hardware cannot do something.
gui comp stream: begin to show hardware excitation/emission settings for filtered colour streams

just the beggining, only the combo box for the excitation is initialised... and don't try with static streams
acq stream: fix metadata update for FluoStream

need to be updated for the new excitation/emission format
gui: consolidate colour theme

put more colour used into the odemi.gui constants
change the log text field to use dark them too.
gui: small clean ups
gui comp stream: show hardware excitation/emission settings for filtered colour streams

Seems to work well, but need more tests with multi-band and static streams.

also fix a bug in band center computation
driver andorcam3: clean up

comment is not true with latests SDKs
gui/acq: make the StaticFluoStream also working with the new stream panel

Should not have differences in the display compared to the original version.
gui stream: fix the filtered coloured stream entry for fixed multi-band filter

should now work in pretty much all the configurations that exist