Add Geometries: Lines, Polygons

[MicheleTobias]

Currently LiteratureMapper only supports points and multipoint geometries. To be really useful we need to add:

• [ ] Line
• [ ] Multiline
• [ ] Polygon
• [ ] Multipolygon

[MicheleTobias]

Idea: Each citation gets text equivalent to a geojson file in the Extra field On opening the plugin, the plugin can sort through the available files and group them up based on the geometry tag (all points into a file, all the polygons in another, etc.) to make the files more easy to work with in a map (i.e. no one wants to deal with 100 files containing one point each).