CLA UX Enhancements

:construction_worker: 

Working on improving the UX surrounding CLAs.

Changes:

- display flash notice below beta banner
- update the agreements content on Manage Profile to be more descriptive (display date and more descriptive button text)
- redirect to ICLA signature and CCLA signature to more useful places
- when viewing an already signed ICLA, display the date and information explaining why one might resign the ICLA
- when viewing an already signed CCLA, display the date and information explaining why one might resign the CCLA
- remove company column from ICLA signatures list
- display name in ICLA sigs list using the signature first and last name to ensure there are no blank names
- change the copy header of Approved Contributors to just Contributors
- remove contributors toggle within companies table and create a separate view for listing the contributors

Working off of this Trello card: https://trello.com/c/pwYhdIHc
I'd suggest a pundit authorizer in `CclaSignatureAuthorizer` that looks something like.

```ruby
def manage_contributors?
  record.organization.admins.include?(user)
end
```

Then in the view you can just do

```erb
<%= if current_user && policy(@ccla_signature).manage_contributors? %>
# link
<% end %>
```

I think that captures the logic you're looking for. Let me know if you'd like to pair on this still or if this helps.