read basic catalog using csv.reader

if the user has a csv file named 'my_catalog.csv' with the form

event_id, time, lon, lat, depth, mag

they should be able to read their catalog in using the following command. right now, loaders that are generator functions are not supported.

```python
import csv
cat = csep.load_catalog('my_catalog.csv', loader=csv.reader)
```