Implement new data sources

[tmcd82070]

Implement the following data sources:

1. Raw CSV files. Two CSV files, one containing transects and one containing sightings. This could be 'guided'.
2. Distance flat files. Add ability to import Program Distance flat files which contain both sightings and transects in one.
3. Shapefiles. Add ability to import three shapefiles for each analysis: (1) POINT file containing sightings; (2) LINES file containing transects; (3) POLYGON file containing the study area. Also could implement MULTIGEOMETRY file to import point transects (i.e., transect lines and points on top of them). The import should be guided and ask for the ID attributes contained in each file, as well as the count and groupsize attributes in the POINT file. After import, the routine could calculate perpendicular distances from points to transects using sf routines. Later, we could take in habitat and landscape covariates to use in the model and in predictions. Output in case of covariates could be shapefiles of density.