ConvertService API improvements

[imagejan]

For some conversions, it would be useful if we were able to hand over some optional parameters, e.g. to specify if a conversion from UnsignedShortType to UnsignedByteType should clip or not, or if a conversion to ImgLabeling should add prefixes to the labels, and if yes, which prefix.

How about a new signature:

ConvertService#convert(Object src, Type dest, Options options)

where these options could be specified?

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Maybe this could even help in distinguishing between lossless and lossy conversions? (See also #288.) Although for this we might also need:

ConvertService#supports(Object src, Type dest, boolean lossless)

or

ConvertService#isGuaranteedLossless(Object src, Type dest)

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/cc @frauzufall @ctrueden