frontend: web-ui: paginate monitor page for more than 1000 packages
    
    When the list of packages is larger than N (1000 currently), instead of
    loading all-in-one page provide a server-side pagination feature.
    
    This required a rewrite of the plain-text SQL query to SQLAlchemy jargon
    to allow the Flask pagination feature.  Having full BuildChroot objects
    in hand, in array - it allowed me to rewrite the templates so they are
    much more readable.
    
    Fixes: #54