Add contextual help for aggregate type selection

Currently, no help is provided when choosing an aggregate type. It makes it very difficult for someone to choose from the existing options.

AC

• Add contextual help in aggregate editor / aggregate type field
• Content:

Use:

• Histograms to apply automatic ranges depending on results (e.g. every 500 dollars, every month)
• Ranges to define your own set of options (e.g. past, future, between X and Y)
• Terms for text and vocabulary entries mapping
• Significant terms to return interesting or unusual occurrences of terms in a set