[Qt-creator] Plugin changes do not 'stick' anymore

[Guido Seifert]

Hi, today the snippet usage with the clang code model was fixed. So I updated my qt-creator repo and cherry picked the fix.
Most likely it is unrelated to the patch, but regardless what plugins I switch on or off in 'About plugins', it does
not survive a restart. If I want to use different plugins I have to use my old qt-creator to change the config. So I 
suppose for some reasons the config files are not correctly written. Permissions are ok, else the older qtc version would 
not be able to change plugins either.

Guido