Add a registration form field for Curriculum Vitae

[juiceo]

We should allow organisers to ask for a Link to CV in their registration form. Essentially this would just require adding a curriculumVitae field in registration-fields.js, very much similar to the Link to Github/Link to Portfolio/LinkedIn fields under the "Links" category.

[juiceo]

This field could also be copied over to the user profile, and editable under /account/profile. Relevant code here: https://github.com/hackjunction/hackplatform/blob/dev/frontend/src/pages/_account/profile/index.js

[Earlo]

Done with #26