Update rcube_install.php

write config file automatically to RCUBE_CONFIG_DIR
Update config.php

write config file automatically to RCUBE_CONFIG_DIR
Update config.php

-Replace tabs with spaces.
-Replace the word "files" with "files", because there is only one
Merge pull request #90 from Dennis1993/master

Write config file automatically to RCUBE_CONFIG_DIR (if writeable)