[Account - Organization] Select the organization by default if only one organization found

[alexchiraples]

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Migrated from https://github.com/gov-ithub/auth-sso/issues/49 Originally created by @alexchiraples on Tue, 15 Nov 2016 14:03:37 GMT

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As an Administrator, I want the organization to be selected by default if I have access to only one organization.

Acceptance criteria:

• If only one organization in the database, OrganizationUsers.SelectedOrganizationId will be automatically set to the organization id if empty
• If OrganizationUsers.SelectedOrganizationId is not null, the left side menu, upper corner will display the selected organization