pam authentication (#5303)
* add pam support, without extra column
* bugfixes for pam login
* document options
* fix code style
* fix codestyle
* fix tests
* don't call remember_me without password
* fix codestyle
* improve checks for pam usage (should fix tests)
* fix remember_me part 1
* add remember_token column because :rememberable requires either a password or this column.
* migrate db for remember_token
* move pam_authentication to the right place, fix logic bug in edit.html.haml
* fix tests
* fix pam authentication, improve username lookup, add comment
* valid? is sometimes not honored, return nil instead trying to authenticate with pam
* update devise_pam_authenticatable2 and adjust code. Fixes sideeffects observed in tests
* update devise_pam_authenticatable gem, fixes for codeconventions, fix finding user
* codeconvention fixes
* code convention fixes
* fix idention
* update dependency, explicit conflict check
* fix disabled password updates if in pam mode
* fix check password if password is present, fix templates
* block registration if account is maintained by pam
* Revert "block registration if account is maintained by pam"
This reverts commit 8e7a083d650240b6fac414926744b4b90b435f20.
* fix identation error introduced by rebase
* block usernames maintained by pam
* document pam settings better
* fix code style
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