Working fix: Enabling pages plugin for new 2.2 installs

(Edit) As Phil commented, legacy support for chunks is not fixed by this simple commit. This request is therefore just a temporary fix for new 2.2 installs, to enable those to use the pages plugin without running into database errors while a permanent fix including legacy support for chunks is worked on.

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I figure adding a simple check for the existence of the chunks database table fixes current issues experienced with fresh installs of 2.2, while maintaining legacy support for chunks for older installs.

Fixes: https://github.com/pyrocms/pyrocms/issues/2211