Integrated widget bad url

### Description
When adding some widget (ethercalc, custom widget ziteboard, awwapp), the shared url seems to not be the same in the integrated widget and in the external link.

### Steps to reproduce
1. create an ethertcalc widget
2. get the ethercalc url of it
3. open an custom widget of this url
4. open an external browser with this url


### Version information

- **Platform**: web (in-browser) or desktop? both

For the web app:

- **Browser**:
Chrome Version 78.0.3904.108 (Build officiel) (64 bits) on Linux CentOS7
Firefox 82.0.2 (64 bits) on Linux CentOS7
Firefox 68.12.0esr (32 bits) on Windows10
Chrome 87.0.4280.88 (Build officiel) (64 bits) on Windows10
- **URL**: develop.element.io & app.element.io

For the desktop app:

- **OS**: Windows10
- **Version**: 1.7.15