Let's make it easy to support new db.engines at install

Signed-off-by: emanuele <emanuele45@gmail.com>
Encapsulate a the install procedure insto a class

Signed-off-by: emanuele <emanuele45@gmail.com>
Moved Settings.php and Settings_bak.php from /install/ to root and changed name to Settings.sample.php and Settings_bak.sample.php; also added a "try to rename files" to the install step

Signed-off-by: emanuele <emanuele45@gmail.com>
Do the same with db_last_error.php, but try to copy it silently, if it fails... who cares (for the moment at least)

Signed-off-by: emanuele <emanuele45@gmail.com>
The less the writable php files we have, the better: db_last_error is just a number, so it can stay in a txt file <= it may be better an hidden file (.db_last_error), but it may be a bit too difficult to find (and removed a global)

Signed-off-by: emanuele <emanuele45@gmail.com>
The install check is now in index.php, no need for having it in Settings and have to remove it and whatever

Signed-off-by: emanuele <emanuele45@gmail.com>