Global Alert

Added a way to show an alert bootstrap style. It is fully customizable (see AlertTrigger propTypes for reference)

here a usage example
```js
var MKAlertTrigger = require("mykoop-core/components/AlertTrigger");

MKAlertTrigger.showAlert("Test alert message");
```
This will generate
![image](https://cloud.githubusercontent.com/assets/4157103/4946694/b390bd04-6617-11e4-8587-d68c6779772b.png)

or the custom version
```js
      MKAlertTrigger.showAlert(
        {
          message: "Test Alert hahaha",
          actionButtons: [
            {
              content: "ok2",
              onClick: function() {
                alert("test");
              }
            }
          ]
        });
```
![image](https://cloud.githubusercontent.com/assets/4157103/4946692/a6f3db6c-6617-11e4-9a91-05dc6652a931.png)


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Perhaps in the  `setState` callback?