Captive form should percent-encode parameters for POST request
I had a problem with connecting to the wifi and I discovered that it was because the form parameters are not correctly encoded before put in the POST request. My wifi password had some character that needed to be encoded to work. It worked when I manually encoded it using encodeURIComponent(<pwd>) and entered the encoded value into the form.

In the file data/captive/app.js these lines:
```
  var params = "ssid=" + document.getElementsByName("ssid")[0].value +
  "&ssidPassword=" + document.getElementsByName("ssidPassword")[0].value +
  "&loginName=" + document.getElementsByName("loginName")[0].value +
  "&loginPassword=" + document.getElementsByName("loginPassword")[0].value
```

should be:
```
  var params = "ssid=" + encodeURIComponent(document.getElementsByName("ssid")[0].value) +
  "&ssidPassword=" + encodeURIComponent(document.getElementsByName("ssidPassword")[0].value) +
  "&loginName=" + encodeURIComponent(document.getElementsByName("loginName")[0].value) +
  "&loginPassword=" + encodeURIComponent(document.getElementsByName("loginPassword")[0].value);
```