Rename Primer default palette as mark17

[nanxstats]

This PR is a follow-up to #62 by renaming the default palette name of the Primer scale from "default" to "mark17".

This makes the palette name more distinguishable (in case of future additions) as these colors appeared under the section "Available mark colors" and were described as:

All chart marks (lines, bars, charts, areas, slices) must meet a 3:1 contrast ratio against the background. If an outline is used, either the outline or the fill must meet a 3:1 contrast ratio.

While there aren't specific rules on contrast between chart mark colors, it is recommended to use colors of different lightness to make them easier to differentiate.