Added escaping for install in config.tpl

In the installation process, string like the one below should be a valid application name (or DB password).
> Framadate c'est vraiment super ! "Datez" comme vous voulez \o/

It missed some escaping for single quote (') and backslash (\\), resulting in PHP parse errors.

It should be cherry-picked to the `release` branch too.

See merge request !136