main: added forceGraph option; also be aware of fixedStation if you play with it!
refactor main, prepare_data: inlined prepareData
main: with getKanjis only the relevant kanjis (jouyou) are considered
utils: allow to pass a offset to equidistantSelection
reworked positioning code to deal with stations instead of kanji
refactor main: split drawStuff into setupInitialEmbedding and setupD3