Smart Float automates the redistribution of floating collections based on available...

Smart Float automates the redistribution of floating collections based on available shelf space and duplicate copies. Smart Float also allows automatic
"re-homing" of items based on a number of circulations from the original library or a specified time frame.

Upon checkin Smart Float will first check if an item needs to be sent home, if not the item will float to the checkin branch if space is available
and there are not too many duplicate titles.  If space and or duplicates don't allow floating to the checkin branch, it will first float to the
branch with most space and no excess duplicates, next to the branch with most space regardless of duplicates.
If no branches have shelf space it will stay where it is (float to the checkin library).

Copy locations are the units of Smart Float operation. Copy locations are mapped to the following attributes that Smart Float uses to determine how to distribute copies.
- active: if true, Smart Float will be used, otherwise traditional floating will occur.
- items_allowed: the number of items the shelving location can hold.
- dups_threshold: the number of duplicate titles allowed for that copy location.
- homing_threshold: number of circulations from the original owning library.
- homing_lifespan: time interval, such as "3 months".
Items will be sent home within the homing_lifespan from creation date, until the homing_threshold is met.
So if shelving location 'kids movies' has a homing_threshold of 1 and a homing_lifespan of "3 months", items in that shelving location won't start floating
until they have circulated once from the owning library, or its been 3 months or more since they were created.

Signed-off-by: Doug Kyle <dkyle@grpl.org>