ignore cacheconfig/*

like for all the other cache sub directories this ignores the content of cache/cacheconfig

changes:
- ignore all files in cache/cacheconfig
- remove cache/cacheconfig/settings.ini.php
- update lhcacheconfig.php to not emit a warning if cache/cacheconfig/settings.ini.php is missing
- <strike>update installation module to try to [touch](http://php.net/touch) the cacheconfig/settings.ini.php if `is_writable` returns false. this will create the file if it is missing or return false if write permissions are really missing.</strike>
- test if writing to cache/cacheconfig is allowed