add ability to load tables without source positions

[cshanahan1]

This PR removes the restriction of requiring source positions (RA/Dec and/or X/Y) when loading tables to allow users to load any sort of table into the data collection. Tables without sources positions will not have linking/mouseover functionality but you can plot them in a scatter/histogram viewer

This also adds some small fixes to improve the automatic detection of ra/dec/x/y columns for some cases i was testing on (related to white space/delimiters)