Add a ChRIS Store account signup in the call-to-action to devs on the front page

[mairin]

There is a call-to-action banner on the front page of the ChRIS store inciting developers to submit their plugins to the store. The sign up form could be placed in this banner, or even just the email submission field (ala GitHub.) This won't replace the pre-existing signup form, just be another potential path in to onboarding a new account.

Sign up form (from chrisstore.co/quickstart):

Current call-to-action banner on the front page:

Example of how GitHub allows signup within a call-to-action (minimal email address submit, that prefills in the larger form on the next screen):

[OladapoAjala]

Hello @mairin can I work on this issue?

[ppk-1996]

@mairin I'll work on this issue. I'll create a PR for it.

[somya51p]

@jennydaman @mairin I wish to look into this one. Please assign it to me.