(Not for merging) online indexing + LPD parallel gain testing

This is to document the branch I intend to tag and deploy for the upcoming SFX@FXE party time. It includes:

• LPD parallel gain
• Tweaks to PeakFinder9 (thanks to Mads)
• Custom user-defined mask addon
• Addon order configurability

Those should all be reviewed and merged independently. This branch is just for merging into so we have everything in one place.