Bug 26529: Define some rules as not able to be blank

Bug 26529: Define some rules as not able to be blank

Currently, the 'Default checkout, hold, and return policy' have a conditional to blank
'holdallowed' when not set, but other rules don't get the same treatment

This patch uses the existing hash that controls the scope of rules and adds a
new parameter 'can_be_blank' Default is assumed to be true, can_be_blank, but if set to '0' then
blank rule values will not be save to the database

To test:
 0 - Set CircControl to 'the library the item is from'
 1 - Goto to Admin -> Circulation and fines rules and select a library
 2 - Under "Default checkout, hold, and return policy" set:
    Total current checkouts allowed: 1
    Hold policy: Not set
    Hold pickup library match: Not set
    Return policy: Not set
 3 - Save the rule
 4 - Check the DB
    SELECT * FROM circulation_rules WHERE branchcode = 'BRANCHCODE'
    using the branchcode for the library you chode
 5 - Note returnbranch, and hold_fulfillment_policy rules exist with blank value
 6 - Set 'All libraries'->'Default checkout, hold and return policy'->'Item floats'
 7 - Checkin an item from the library with blank rules at another library
 8 - It returns home rather than floating
 9 - Apply patch and restart all the things
10 - Reload the page and save the rules as before
11 - Check the DB and note the rules no longer exist
12 - Check in the item, it floats!
13 - prove -v t/db_dependent/Koha/CirculationRules.t

Signed-off-by: Andrew Fuerste-Henry <andrew@bywatersolutions.com>
Signed-off-by: Martin Renvoize <martin.renvoize@ptfs-europe.com>
Signed-off-by: Jonathan Druart <jonathan.druart@bugs.koha-community.org>