Added fullscreen button; Added webgl web links; Upgrade xterm, addon-fit;

[npoh]

• Added fullscreen (translucent) button for terminal
• Added xterm addons webgl 0.16.0, web links 0.9.0
• Upgrade xterm to 5.3.0, addon-fit to 0.8.0

Instructions for installing this version for general users:

mkdir temp-dir
cd temp-dir/
wget https://github.com/npoh/webssh/archive/refs/heads/fullscreen.zip
unzip fullscreen.zip
mv webssh-fullscreen webssh

pip uninstall webssh # uninstall any previous version
pip install webssh/
cd ..
rm -r temp-dir/