One last thing, have you considered adding a test to ModelListWidget_TEST for the plugins? A simplified version of ModelListWidget_TEST::LinkProperties loading world/underwater.world and checking the buoyancy plugin properties should be enough, does that sound doable?
Queued a new trusty gpu build, but checking it locally I realized there is one failing test, could you fix it please?
FAIL! : ModelListWidget_TEST::LinkProperties() Compared values are not the same
Actual (sphereLinkItem->text(0)): box_link
Expected (tr(sphereLinkName.c_str())): sphere_link
Note to reviewer: This pull request introduces a transport request for model_plugin_info, which takes a model plugin's URI in string format. The plugin URI is being assembled by its parent model's URI. It's the first time a request is using URIs and the first time plugin URIs are being used at all.