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
Restrict display of Link to Orphan button to active sponsors
Fix up sponsorship_steps.rb
Create & use Sponsor#eligible_for_sponsorship method
Fix sponsorship_steps.rb & cleanup
Code review: method names end with ?, improve readability of specs
Merge pull request #60 from NikitaAvvakumov/limit_sponsorships_to_active_sponsors

Limit sponsorships to active sponsors
move model-specific initializer methods from initializer.rb to models

OSRA-152 #Code-Review
renamed methods for clarity after code review

OSRA-152 #Code-Review #comment renamed methods after code review
Merge pull request #62 from PurityControl/initializer_refactor

OSRA-152 #resolve xxxxxx #comment xxxxxxxx
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