CellWorX/Metaxpress: Read metadata from one file per channel, to preserve all channel data

[melissalinkert]

Backported from a private PR.

To test, use metaxpress/samples/multi-channel-test/multi-channel.HTD. Without this PR, showinf -nopix -omexml should show 2 channels in the OME-XML, but only the first has an EmissionWavelength. With this PR, the same command should show that both channels have an EmissionWavelength set, and that the two wavelengths are different. The wavelengths can be compared against the configuration for the original pixels files (see metaxpress/samples/multi-channel-test/readme.txt).

[sbesson]

A few failing tests - see https://merge-ci.openmicroscopy.org/jenkins/job/BIOFORMATS-test-folder/178146/console - which will require some configuration updates

[melissalinkert]

Should be fixed by https://github.com/openmicroscopy/data_repo_config/pull/521/commits/f69aee2353d837b467e854215bb0f94dd7dd9900

[dgault]

Builds and tests have been green with this PR and the config PR included.

Tested using the recommended sample file from metaxpress/samples/multi-channel-test.
Without the PR the sample file showed 2 channels, only the first containing EmissionWavelength:

         <Channel EmissionWavelength="488.0" EmissionWavelengthUnit="nm" ID="Channel:0:0" Name="DAPI" SamplesPerPixel="1">
            <LightSourceSettings ID="LightSource:0:0" Wavelength="488.0" WavelengthUnit="nm"/>
            <DetectorSettings Binning="1x1" ID="Detector:0:0"/>
            <LightPath/>
         </Channel>
         <Channel ID="Channel:0:1" Name="FITC" SamplesPerPixel="1">
            <LightPath/>
         </Channel>

With the PR both channels have EmissionWavelength populated and the values for each channel are different and correct:

         <Channel EmissionWavelength="488.0" EmissionWavelengthUnit="nm" ID="Channel:0:0" Name="DAPI" SamplesPerPixel="1">
            <LightSourceSettings ID="LightSource:0:0" Wavelength="488.0" WavelengthUnit="nm"/>
            <DetectorSettings Binning="1x1" ID="Detector:0:0"/>
            <LightPath/>
         </Channel>
         <Channel EmissionWavelength="568.0" EmissionWavelengthUnit="nm" ID="Channel:0:1" Name="FITC" SamplesPerPixel="1">
            <LightSourceSettings ID="LightSource:0:0" Wavelength="568.0" WavelengthUnit="nm"/>
            <DetectorSettings Binning="1x1" ID="Detector:0:0"/>
            <LightPath/>
         </Channel>