Cleanup GUI plugin menu

[chapulina]

Environment

• OS Version: all
• Source or binary build? all

Description

• Expected behavior:

  Inserting a plugin from the top-right menu should never crash. When inserting a plugin that doesn't have any widgets, we should add some text explaining to the user that this is the case, otherwise the user may think they're doing something wrong, or something is broken.

• Actual behavior:

  Inserting plugins like Scene3D crash the application... Plugins like KeyPublisher are empty.

Steps to reproduce

Insert various plugins from the menu and see how some behave badly.

[chapulina]

Progress tracking

Citadel

Plugin	Status
Component Inspector	ok ✔️
Scene 3D	crash 💥 gazebosim/gz-gui#347 ✔️
Teleop	ok ✔️
Entity tree	ok ✔️
Video Recorder	ok ✔️
Grid 3D	Empty gazebosim/gz-gui#363 ✔️
Shapes	ok ✔️
Grid config	ok ✔️
Topic Viewer	ok ✔️
Gz Scene 3D	Empty, eventual crash 💥 #1294 ✔️
World control	Empty gazebosim/gz-gui#349 ✔️
Image display	ok ✔️
Screenshot	ok ✔️
Joint position controller	ok ✔️
Tape measure	ok ✔️
Key publisher	Empty gazebosim/gz-gui#362 ✔️
Topic echo	ok ✔️
Playback scrubber	ok ✔️
Transform control	ok ✔️
Plot 3D	ok, but lots of warnings are printed ✔️
View angle	ok ✔️
Publisher	ok ✔️
World stats	Empty gazebosim/gz-gui#349 ✔️
Resource spawner	ok ✔️
Align tool	ok ✔️
Shutdown button	ok ✔️

Fortress

Only plugins that aren't on Citadel

Plugin	Status
Banana for scale	ok ✔️
Camera tracking	Empty gazebosim/gz-gui#366 ✔️
Visualize contacts	ok ✔️
Transport scene manager	Freeze 🧊 gazebosim/gz-gui#365 ✔️
Copy paste	ok ✔️
Entity context menu	Empty #1375 ✔️
Select entities	Empty #1375 ✔️
Gz Scene manager	Crash 💥 #1371 ✔️
Interactive view controller	Empty gazebosim/gz-gui#366 ✔️
Joint position controller	ok ✔️
Spawn	Empty #1375 ✔️
Lights	ok ✔️
Marker manager	Empty gazebosim/gz-gui#366 ✔️
Transport plotting	ok ✔️
Minimal scene	Freeze / crash 💥 gazebosim/gz-gui#364 ✔️
Nav Sat Map	ok ✔️
Visualization capabilities	Empty #1375 ✔️
Visualize lidar	ok ✔️
Plotting	ok ✔️

[chapulina]

All PRs merged. No plugins should crash / freeze or be empty on insertion now. We should be careful not to add new plugins that break these rules.