Remove company column and adjust name display in sigs list

Remove the company column displayed in the table of ICLA signatures.

When viewing the list of ICLA signatures on production, there appear to be some
blank names. Using the first and last name (required fields of the signature)
ensures that it will not be blank.
Change Approved Contributors copy to Contributors.
Display message when re-signing CCLA.

When viewing the form for re-signing a CCLA, let the user know that is what they
are doing!
Move the CLA companies contributors listing into their own view.

Currently, the way contributors on behalf of a company are displayed is a
show/hide toggle button with in the table of companies. This results in a funky
looking and difficult to read table. This changes the button to display the
contributors to link to a new view that lists all of the contributors.

Above that table is a button to return to the companies listing, as well as
context sensitive buttons:

- one for viewing the CCLA if the current user is a member of that company
- one for going to the invitations management view for that company
Fix typo in ccla_signatures_controller docs.
Remove the company attribute from ICLA Signatures.

When the ICLA is signed, the user's company matters not.

This adjusts the mailers for CCLA signatures and ICLA signatures to use their
own footers because company was removed from ICLA signatures.
Update CLA flash messages to be consistent.

Make the CLA flash messages regarding signing, resigning and not being able to
sign a new one more personalized and consistent with the rest of the app.
Add authorizer methods + specs for CclaSignatures

Expand upon the authorizer methods, their docs and their specs. Use them for the
view logic.
Only CCLA admins can see Manage Contributors tab.
Make CCLA sig viewing read-only for non-admins.

Only admins of CCLA organizations should be able to update (re-sign) CCLA
organization signatures. You don't want any old Bart Fart going in and making
your phone number something dumb like 1-800-OMG-BUTT or something right?!?!
Increase the tab margin bottom override.

In Firefox on Ubuntu, the line was still showing under the active tab. This
fixes that!
Create partial for CCLA org nav tabs.

In order to reuse the CCLA org nav tabs for viewing the CCLA signature, viewing
Contributors and managing Contributors, move it all into a partial that can be
used where we need it. This partial includes logic with authorizers for
determining who can see what.

One place this is being used in a different way is when a user is viewing the
list of Contributors for an Organization. If the user is part of that
Organization, they will see the nav tabs for that Organization. If the user is
not part of that Organization, they will see a link bringing them back to the
list of Organizations (companies).
Fix admin typo on CCLA sig show
Add details about signing a CCLA above the form.

Suggest that people look for their company before signing a new CCLA. If their
company exists, suggest that they reach out to an admin for an invite. [This
will change once we have the ability to request to join, but for now it should
work].

This also adds a little [admin] note next to CCLA organization members who are
admins so folks know who to reach out to in order to get an invite!