Bug - "Add column" button visible on boards you are not allowed to administer

[alexandreruban]

Context

In #1906, you made sure that only users who can administer the board can add columns. However, you didn't remove the "+ Add column" button from the screen for users who can't administer the board.

Steps to reproduce

1. Login as JZ
2. Visit the Fizzy board
3. Click on the "+ Add column" button
4. Fill a name and click "Add column"
5. Nothing happens

In the server logs, we can see a 403 is returned:

Processing by Boards::ColumnsController#create
...
Filter chain halted as :ensure_permission_to_admin_board rendered or redirected
Completed 403 Forbidden in 10ms (ActiveRecord: 0.4ms (5 queries, 0 cached) | GC: 0.0ms)

Suggested fix

The "+ Add column" button should be hidden for users who can't administer the board.

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Note 1: I'd be happy to work on this issue if you can reproduce on your side.
Note 2: Thanks for open-sourcing fizzy. It's always a pleasure to read 37signals code 😊

[alexandreruban]

I'm closing this since the commit was reverted in #1922.