Add option to import datasets from online databases

[RiboRings]

There are many R packages that make online datasets accessible in the form of TreeSE objects. A list is provided in the OMA chapter on Data Import. While the iSEEhub and iSEEindex extensions of iSEE can be respectively used to fetch data from ExperimentHub or custom databases, there is no direct way to analyse datasets from MGnify, HoloFood, curatedMetagenomicDatasets and MicrobiomeData sources. These import options could be added to the Dataset bar in the Import box, which currently only provides mia datasets as possible input.

[RiboRings]

Being a shiny app, miaDash might significantly slow down when importing datasets from a database like MGnify.

Instead, we can shift the focus towards making manual import as smooth as possible by supporting database formats.

For example, this was done for MGnify here: 22dcfd3