basic recommendation system

[yarikoptic]

We have one more poster session to go so it could still be useful

I think poster presenters still do not quite get the fact that there would be little to no attendance if everyone just stayed by their own poster. I think it would be useful to recommend them some to go visit while they are at theirs waiting for visitors. Thus particularly relates to #127 - if there was some listing of posters related to the current one visited. Finding recommendations could be done very crudely e.g. through % overlap between keywords which we already have for each poster in abstract field for each poster in abstacts.json, and placing e.g. 5 top hits within posters.json for each poster. But I would not be able to provide UI for that ;) @soichih - what do you think?