Feat/use calc centroid

[robitalec]

Using calc_centroid throughout functions, see #116

For centroid_group, centroid_dyad, and centroid_fusion:

• provide alternative sfc interface for centroid functions
• if coords are provided, crs is provided or NULL
• if coords are NULL, use default "geometry" sfc interface and ignores crs
• use env argument for programming on data.tables (Fix: Use data.table's env argument #95)