Spreadsheet importer detail so usage from toolkit will be easier and automatic as before for all CSV file types.

#1562 Implement VizualizationController.selectNodes/selectEdges: Fix null pointer exception and synchronization issues with octree usage

Fix #1511 Filter is changed after saving file and opening again
Fix #1458 Filter settings incorrect and causing crashes after reloading a .gephi file

#1706 Clarify how pagerank works in the code and improve performance. Also adapt code to correctly take into account parallel edges so each neighbor is not processed several times (+ ignore self loops too).