Add AWS S3 javascript based upload.

This changes add button at the bottom of editor.

![2014-02-07_20-58-47](https://f.cloud.github.com/assets/650741/2111014/b8711694-900b-11e3-9482-da57f07cb011.png)

If you click this button, file select dialog allow you to chose picture. After it is selected it immediately upload it to Amazon S3 bucket and insert as markdown code. Plugin has new set of parameters.

![2014-02-07_21-24-39](https://f.cloud.github.com/assets/650741/2111051/46f9bd80-900c-11e3-9a2e-76edf90d3e18.png)

It works like here on github. In the future I'll add drag and drop ability too.