OSRA-120 Create and Add Another Sponsor (AA)

[NikitaAvvakumov]

https://osraav.atlassian.net/browse/OSRA-120

• add 'Create and Add Another' button to New Sponsor view
• override admin sponsors_controller#create to parse params[:commit]
• write Cucumber scenario & controller spec

[razorcd]

:+1:

[gmunumel]

:+1: