update the layout manager to support geometry constraints

this adds support to the layout manager to support boundary constraints
on a widget in addition to size hint constraints
update backend constraints widgets for boundary constraints
update backend containers for geometry constraints
update geometry guard naming
update geometry guard naming
update the dynamic fields example for layout updates
remove hug_height declarations which are no longer needed
pep8 formatting
remove hug declarations which are no longer required
more appropriate constraint weight
remove unnecessary hug declarations
remove unnecessary hug declaration
remove unnecessary hug declarations
pep8 formatting
cleanup constraints generation
pep8 formatting
cleanup flow area example
pep8 formatting
remove unnecessary hug_height declarations
use a Form to simplify the example