Refactor (break up) the big monolithic install_moodle.sh & setup_webserver.sh

Currently `install_moodle.sh` and `setup_webserver.sh` require a bunch of command line arguments for a single site, which grow more and more and won't be sustainable sooner than later. Ideally those command line parameters should be packed in a config file and passed down to the VM deployment template. It might require using cloud-init as mentioned in #33. I'm raising another issue, because this will also help supporting multiple Moodle sites with a single deployment (#78). Eventually we'd want a config file (for multiple Moodle sites) created/shared/updated on `/moodle` and let each VMSS VM instance configure its html directories, moodledata directories, and Apache virtual hosts as stated in the config file. The controller VM will need to create that config file based on the deployment-time custom data (for cloud-init) that should replace the `install_moodle.sh` cmdline parameters, and probably the script itself with something more flexible like a Python script (to facilitate processing the custom data and config file generation better).