slow upload for large ontology

[adhamhashibon]

we need to think of how to handle large ontology/results of search.

the solutions could be multiple stages:

1. have a hard limit on the number of nodes, add a counter and cut off what is visualised,
2. in case of 1, would be good to show a note to the user, so that they can limit their query or search.
3. [advanced] allow sort of pagination? or show only is-a relations for all data, and have a filter for adding removing other relations, so that we do not show a large group. we need more thought on this! @chichiariscelavia @ChungTingLao what do you think?

[ChungTingLao]

I think the default option should be simple and fast for new users and demonstration purposes (e.g. is-a only, limited depth). We can then provide advanced options to do in-depth search, with warnings about response time.