Server name not escaped in front end setup

When entering a server name in the frontend initial setup, it is not escaped, and accepts special characters. This causes invalid syntax in the config file, and the frontend refuses to load.

eg. entering:
Grant's Test Server
becomes:
$ZBX_SERVER_NAME = 'Grant's Test Server';

The extra ' breaks it.

The field should either escape the ' (if it won't cause problems elsewhere), strip it out, or prompt the user with an error.