New workflow when a voucher votes No for an applicant

[hugosolar]

Fixes #370

Description
This pull request modifies the current workflow as described here :

• When a voucher votes No for an applicant
  • Trigger a notification mail to the applicant which inform that the application needs to be reviewed by the Membership Committee
  • Change the applicant status and mark with purple color. also shows the applicant in the application for approval screen in the backend section.
  • new Gravity form added to provide the MC a way to review the application
  • If the MC determines the applicant can continue with the application, an email with a note is sent to the user. The applicant has the chance to choose new vouchers and the applicant status is changed to update-vouchers.
  • If the MC determines the applicant can't continue with the process, the application is rejected (same process to reject any application)

Other information

Checklist:

• My pull request has a descriptive title (not a vague title like Update index.md).
• My pull request targets the master branch of the repository.
• My commit messages follow best practices.
• I added tests for the changes I made (if applicable).
• I added or updated documentation (if applicable).
• I tried running the project locally and verified that there are no
  visible errors.

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