Proj databrowser trace types

This was started off the 3.2.x branch, but with the 3.2.11 release that close, might be better to leave 3.2.x untouched and instead merge this into master for the next release.
Tried a test merge into master, no problems.

This adds a new trace type option to the data browser, #167 .
Existing *.plt configs are not affected.

Once 3.2.11 is released, this could be added via hot fix.