Check for Android SDK/NDK being writable

When I installed (unzipped) the Android SDK and NDK to /opt that was owned by root:root, Qt Creator was not able to use the SDK properly. It was giving me error messages that packages were missing but then failed to install them. Also the sdkmanager tab at the bottom was empty and all the buttons down there gave error messages.

Maybe Creator could check for the SDK/NDK being in writable locations and warn about it, if not.