Multiple storage of APIs

Hello!

I needed to manage more than one API at time, and downloading and uploading files was a little repetitive. So I've added a new function in the header to allow  loading of different YAMLs storaged in the localstorage of the browser.

Now the YAML loaded in the Editor is saved as **yaml** (as it was before) and then specifically with the title of the api. So by doing this is possible to maintain several APIs at once!.

This can be tested on: http://www.gsole.cat/swagger-editor

Gerard

PS: petstore-api.herokuapp.com yaml I think that is failing in new versions, I think that I read about that.
PS2: I don't know why travis is not passing the tests, I imagine that it is not my fault. Now in my dev machine (Linux) I tried again, but it breaks in:

```js
Running "protractor:main" (protractor) task
util.puts: Use console.log instead
Starting selenium standalone server...
/home/gerard/swagger-editor/node_modules/protractor/node_modules/selenium-webdriver/lib/webdriver/promise.js:1643
      throw error;
            ^
Error: Timed out waiting for the WebDriver server at http://192.168.3.143:47788/wd/hub
    at Error (native)
    at onResponse (/home/gerard/swagger-editor/node_modules/protractor/node_modules/selenium-webdriver/http/util.js:87:66)
    at /home/gerard/swagger-editor/node_modules/protractor/node_modules/selenium-webdriver/http/util.js:42:21
    at /home/gerard/swagger-editor/node_modules/protractor/node_modules/selenium-webdriver/lib/webdriver/http/http.js:96:5
    at ClientRequest.<anonymous> (/home/gerard/swagger-editor/node_modules/protractor/node_modules/selenium-webdriver/http/index.js:136:7)
    at ClientRequest.emit (events.js:107:17)
    at Socket.socketErrorListener (_http_client.js:271:9)
    at Socket.emit (events.js:107:17)
    at net.js:436:14
    at process._tickCallback (node.js:343:11)

```