Map - issues with barplot marker previews

[bobular]

Please check this is still a live issue after #190 is completed (and remove the question label).

Issue 1

The logscale mode for the preview bar marker doesn't seem to be right.

Here are no-logs markers - the preview looks similar to the three map markers:

Here are logged markers - now they don't look at all similar:

Originally posted by @bobular in #285 (comment)

Issue 2

The proportion mode is not working in the bar marker preview since the data for the marker preview is coming from the subsetting service, which does not support valueSpec: 'proportion'

[bobular]

Still an issue. Making this required for beta