Union atom types

[breck7]

We have an atom type here that can be a column name or a color. Need to support types like that.

❌ 4 errors in "/Users/breck/scroll/blog"
filename type line atom suggestion path message
dataScience.scroll InvalidAtom 123 1 sampleData parseDate linechart stroke InvalidAtom at line 123 atom 1. "steelblue" does not fit in atomType "columnNameAtom".
dataScience.scroll InvalidAtom 136 1 sampleData groupBy barchart fill InvalidAtom at line 136 atom 1. "teal" does not fit in atomType "columnNameAtom".
dataScience.scroll MissingAtom 177 3 sampleData splitYear groupBy reduce MissingAtom at line 177 atom 3. Missing atom for atom "newColumnNameAtom".
dataScience.scroll InvalidAtom 196 1 iris barchart fill InvalidAtom at line 196 atom 1. "teal" does not fit in atomType "columnNameAtom".