Add 'version' to the Page Model API _meta section

Since we will make changes to the Page Model API output, the (SPA) client should be able to get from the page model api result the version number. Most likely we will also have to include the version in the URL

Note that the HST for for example version 14.1, most likely will be possible to configure to serve the Page Model API version 1.0 and also 2.0 : 2.0 will have some incompatible changes

Also note that the version should be there as a string value, not a number