Implement an all.equal() method for SummarizedExperiment objects that performs a "deep comparison"

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all.equal() on SummarizedExperiment objects needs to perform a "deep comparison" in order to avoid false positives or false negatives. In particular this means that it must perform a deep comparison between the assays slots of the 2 objects. This deep comparison will be expensive when the assay data is on disk but hey, the end user should realize that s/he is asking for a deep comparison so should be ready to pay the cost.