Visualize keywords (or other entry fields) as bubble matrix

[tobiasdiez]

Often one has two different dimensions (year + keyword, or two types of keywords [refs #628]) and one is interested in how papers are distributed along these dimensions. Helpful especially for literature reviews.

Real "life" example:

from https://www.researchgate.net/publication/305209288_Evidence_in_Architecture_Degradation_and_Consistency_Checking_Research_-_Preliminary_Results_from_a_Literature_Review.

More examples of bubble matrix diagrams (in different contexts):

There are nice libraries for d3 https://github.com/benbria/d3.chart.bubble-matrix and https://github.com/gusgard/d3-bubble-matrix. These can be used once we switch to javafx -> tagged as after-javafx and closed for the moment.