User can toggle between login pages

[maggie-larkin]

h4. Notes

• See here for design, no need to worry about the cute graphics at the moment
• Some of this functionality exists here but this would allow the toggle between foster and volunteer

h4. User Story
As a volunteer for The Little Black Dog
I want to log into the system
So that I can see the list of fosters

h4. Acceptance Criteria
GIVEN I am on the login page
THEN I see a section that says "Login"
AND underneath that there's a toggle that says "Foster" and a toggle that says "Volunteer"
AND the default is to the "Foster" toggle being selected