FRCSim, Gazebo v7, and GearsBot example

[mrosen]

I also ran into the missing libboost_system_1.54.0.so problem. I entered a ticket against it here: https://github.com/wpilibsuite/allwpilib/issues/452

My work around is to rebuild the plugins (along with the rest of the library):

1. Clone the updated repository from WPI "allwpilib".

2. Make sure Gradle is installed ("sudo apt install gradle")

3. From the "allwpilib" directory, build using Gradle; "./gradlew build -PmakeSim"

4. Copy the newly build plugins from ~/allwpilib/build/install/simulation/plugins (where Gradle just built them) to ~/wpilib/simulation/plugins (where they are referenced from the "frcsim" script that starts Gazebo for us.

I'm able to get example GearsBot simulation model to move in response to the corresponding default "Gearbot" example program. I'm finding it slow and difficult. I would love to hear about other's experiences here.