Improved injecting of settings from a default blog to new blogs

This wasn't always working well with the new auto-options logic.
It should now work as expected for multisite individual activations, network activations, new blogs on the network.

The only case in which it will not always work well is with multisite and WPSEO in the must-use directory.
Added note to admin page about not importing privacy sensitive options and such
Updated network page text - site not blog