Allow is_network_activated to be filtered

[joehoyle]

Currently there's no way to filter the network activated detection (bar filtering the option plugins activated value). This means unless the is_mustuse is triggered, you can't get the network wide behaviour when loading Stream in other ways.

I refactored this into a method that is consistenty used on the Plugin class, and also added a filter. Forcing network behaviour is then just a case of doing add_filter( 'wp_stream_is_network_activated', '__return_true' );

[kasparsd]

Thanks so much @joehoyle! Is this ready for code review?

[kasparsd]

Looks great!

Travis errors are due to wp-dev-lib using the latest version of WordPress 5.2 which doesn't support PHP below version 5.6:

Your server is running PHP version 5.4.45 but WordPress 5.2.1-src requires at least 5.6.20.

So we're OK to ignore that.

[joehoyle]

Yup, good stuff!

[rheinardkorf]

Very elegant! Thanks @joehoyle :)