webserver: move to a module, fix and remove a few things

- Renamed webserver::base to webserver::sysctl_settings
- Removed completely webserver::apache::php5-{mysql,gd}

Change-Id: I8123d618e3ef8a56ee8bb65b21cbb95f45cbb664
Signed-off-by: Giuseppe Lavagetto <glavagetto@wikimedia.org>