Create graphical Mahara pre-installer

[Aaron Wells]

Most polished PHP applications come with a graphical pre-installer, which does an environmental sanity check and generates your config file for you. This helps welcome in new users and those who are investigating the software to decide if they want to use it. Mahara does not currently have one of these. Instead, it sniffs for the presence of a config.php, and if it doesn't find it, it tells you to write one by hand, by copying config-dist.php. And that works well enough, but it's not a very welcoming experience.

The pre-installer should work something like those for other popular PHP web applications (such as Moodle & Piwik):

1. When Mahara detects no config.php present, it sends you to the preinstaller
2. (Optional) The preinstaller asks you which language you want to proceed in
3. The preinstaller presents you with a form that asks you to fill in the minimum fields for your site. For Mahara these would be:

 - DB connection parameters (not including dbprefix)
 - Dataroot
 - wwwroot (pre-filled based on current URL)

4. Sanity check these options. Mahara would check to make sure the DB connection works and has the right permissions, and it would check that the dataroot is writeable and try to detect whether it's accessible from a URL. It would also access the wwwroot and make sure it is this self-same Moodle site.

5. Generate the config.php file. Using a template file, or find/replace in config-dist.php, Mahara would generate the body of a sample config.php file for the site. It should also prefill the password salt config option, with an appropriate randomly generated salt.

6. Tell the user where to put the config.php, or write it to the right place.

7. Then hand things over to the installer, and proceed as normal.