Add ExternalURL disabled on new versions

[sachgits]

Issue description

External URL disabled

Steps to Reproduce

1. go manage content
2. go to other videos
3. click create generic video
4. fill in the popup form for video
5. click save
6. find the newly added generic video and open
7. click on Drop file or click here to add
8. click on External Url

Expected Behaviour

paste externallink when uploading videos and subtitles

Actual Behaviour

Add ExternalUrl button is disabled

Environment Information

• Operating System: docker openjdk8
• Streama version: v1.10.5
• Custom streama build, describe customizations or provide link to fork (If Applicable):
• Container Version (If Applicable):