Change notice message for inactive WSAL plugin

[Martin Krcho]

Note: Please work on this issue after issue #29.

If the WSAL plugin is installed on site, but not active, each active extension plugin shows an admin notice like this:

We should change this to say:

The {plugin name} extension requires the WP Activity Log plugin to work, which is already installed on your website. [Activate the WP Activity Log plugin]

[sdobreff]

/cib

[create-issue-branch]

Branch issue-30-Change_notice_message_for_inactive_WSAL_plugin created!