SDK docs now a separate plugin


I moved the SDK help contents to a separate plugin as it was bloating the SDK Core plugin quite a bit (about 7MB). If you use nightly and want to keep the manual you will have to select the plugin and install it from the next update on. The plugin will always be installed in the next SDKs so there is no need to do that from the next release on. Theres basically no change except that when the SDK Core features update you do not need to update 7MB of documentation and images as well :wink: