Pre-selected authentication method in login form

Note: this PR affects only the case when more then one authentication method is specified in configuration.

The PR propose to display to user in log-in form a pre-selected authentication method. Pictures below illustrate this.
First picture is before changes, second picture is after changes.
Also, to retain possibility to display "hard" method selection, a parameter to loginAction function is added.

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![Image 1](https://f.cloud.github.com/assets/628801/275124/9b2210ae-907d-11e2-9e3c-4cdac88adfe3.png)

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![Image 2](https://f.cloud.github.com/assets/628801/275125/9f0247ac-907d-11e2-8ce5-7aa76802c727.png)
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| Q             | A
| ------------- | ---
| Bug fix?      | no
| New feature?  | yes
| BC breaks?    | no
| Deprecations? | no
| Tests pass?   | yes
| Fixed tickets | no
| License       | MIT
| Doc PR        | no