added migration and test to see field seen in model

part of PT story https://www.pivotaltracker.com/story/show/79157380
(while testing jira for sprint 3 part of OSRA_-83, OSRA-84 and OS-1)
created requested_sponsor_count field in active admin views

part of PT story https://www.pivotaltracker.com/story/show/79157380
(while testing jira this relates to OSRA-83 subtask OSRA-85 #resolved
field shown in
- show
- create
- update
made requested_orphan_count field mandatory and be a positive integer

part of pivotal tracker story https://www.pivotaltracker.com/story/show/79157380

- added new constraints to requested_orphan_count_field
- refactored tests and factories to comply with new requirements

OSRA-86 #resolve
OSRA-83 #resolve
change factory girl to randomise value for requested_orphan_count

OSRA-83 OSRA-84 OSRA-85 OSRA-86 #code-review
OSRA-83 #comment sponsor factory requested_orphan_count randomised
fixed incorrect generation of random data for sponsor factory

OSRA-83 OSRA-84 OSRA-85 OSRA-86 #code-review
OSRA-83 #comment sponsor factory requested_orphan_count randomised
Merge pull request #61 from PurityControl/requested_orphan_count

OSRA-83 #resolved
OSRA-84 #resolved
OSRA-85 #resolved
OSRA-86 #resolved