Install plugins into lib tree

[SammysHP]

Install plugins into ${CMAKE_INSTALL_PREFIX}/lib/plotjuggler-plugins for non-ROS installs, which would be the appropriate location on Linux systems.

The previous value bin was ambiguous anyway. Not sure if this is how you like it or if you have a "portable" version of PlotJuggler in mind. I kept reading the executable directory for backwards compatibility.

Fixes #1153

[facontidavide]

have you checked that PlotJuggler can actually find the plugins? I am not sure it will

[SammysHP]

It does, because I've added PJ_PLUGIN_INSTALL_DIRECTORY to the search paths in mainwindow.cpp.

$ plotjuggler
Warning: Ignoring XDG_SESSION_TYPE=wayland on Gnome. Use QT_QPA_PLATFORM=wayland to run on Wayland anyway.
Loading compatible plugins from directory:  "/usr/bin"
"/usr/bin/ld.so" :  "Failed to extract plugin meta data from '/usr/lib/ld-linux-x86-64.so.2'"
Loading compatible plugins from directory:  "/usr/lib/plotjuggler-plugins"
"/usr/lib/plotjuggler-plugins/libDataLoadCSV.so is a DataLoader plugin"
"/usr/lib/plotjuggler-plugins/libDataLoadMCAP.so is a DataLoader plugin"
"/usr/lib/plotjuggler-plugins/libDataLoadULog.so is a DataLoader plugin"
"/usr/lib/plotjuggler-plugins/libDataStreamMQTT_Mosquitto.so is a DataStreamer plugin"
"/usr/lib/plotjuggler-plugins/libDataStreamSample.so is a DataStreamer plugin"  ...disabled, unless option -t is used
"/usr/lib/plotjuggler-plugins/libDataStreamUDP.so is a DataStreamer plugin"
"/usr/lib/plotjuggler-plugins/libDataStreamWebSocket.so is a DataStreamer plugin"
"/usr/lib/plotjuggler-plugins/libDataStreamZMQ.so is a DataStreamer plugin"
"/usr/lib/plotjuggler-plugins/libParserDataTamer.so is a MessageParser plugin"
"/usr/lib/plotjuggler-plugins/libParserLineInflux.so is a MessageParser plugin"
"/usr/lib/plotjuggler-plugins/libParserROS1.so is a MessageParser plugin"
"/usr/lib/plotjuggler-plugins/libParserROS2.so is a MessageParser plugin"
"/usr/lib/plotjuggler-plugins/libProtobufParser.so is a MessageParser plugin"
"/usr/lib/plotjuggler-plugins/libPublisherCSV.so is a StatePublisher plugin"
Type conversion already registered from type QString to type QwtText
"/usr/lib/plotjuggler-plugins/libToolboxFFT.so is a Toolbox plugin"
"/usr/lib/plotjuggler-plugins/libToolboxLuaEditor.so is a Toolbox plugin"
Type conversion already registered from type QString to type QwtText
"/usr/lib/plotjuggler-plugins/libToolboxQuaternion.so is a Toolbox plugin"
Loading compatible plugins from directory:  "/home/sammyshp/.local/share/PlotJuggler"
Plugin folder does not exist:  "/home/sammyshp/.local/share/PlotJuggler"
Current version: "3.14.3" . Latest release version : "3.14.3"
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