/country/add: deny "add" and "list" as country names

[php-coder]

Steps to reproduce:

• login as a user
• create country with name (in English) "add" (or "list")

Expected result:

• error message is shown because of invalid name

Actual result:

• country has been created and user was redirected to /country/add (or /country/list) page

[php-coder]

I suggest to add validator DenyValues and pass disallowed values into it:

@DenyValues({"add", "list"})
private String name;

[php-coder]

@n583wxdh0j Are you still working on this issue? If not, let me know and I'll reassign this issue to someone else.

BTW validator is mostly implemented as part of #509 that will be merged soon.

[n583wxdh0j]

Give me a week.