Change form name of GeneralConfigPage to "setup_general_config"

Used to be "setup_application_config".

refs #7163
Let the setup's view scripts be a bit more generic

refs #7163
Make it possible to differentiate the "final" next button

refs #7163
Add install routines for all INI files

This is just a quick&dirty implementation. Once we know how modules are
being processed/installed this needs to be revisited.

refs #7163
Drop dependent page data more earlier

Not only the "setup_authentication_backend" page depends on the auth
type but also the "setup_admin_account" page, so just drop both entries
once a new auth type gets submitted.

refs #7163
Silence file_get_contents call

Since an earlier change already made the existence of config files not
required we do not care about any E_WARNING or notice emitted by
"file_get_contents".