Install script using --system-site-packages

Changes to the install script "install_trixie.sh"
In some conditions /boot/firmware/config.txt was getting overwritten instead of appended to.
And the virtual environment that gets created now use --system-site-packages

better handling for user created venv

better handling when install_trixie is called in an already existing venv created by user.

Trixie Support

some minor changes to the install script, such as setting SPI and I2C , and VNC for the end user.

Move launch_brickpi3_troubleshooter.sh to $HOME

Getting launch_brickpi3_troubleshooter.sh out of the BrickPi3 git repo allows that repo to stay clean, enabling easy future pulls.