kolibri: Cannot import a second channel from Studio in IE11

Observed behavior

Noticed while testing the 0.13.1b1.

When using IE11 it seems to be possible to import resources only from one public channel on Studio, as when you make a second attempt and press the Select resources button for any other channel, nothing happens (user would expect to see the channel topic tree loading at this point).

• It is still possible to import unlisted channels using the token.
• If user stops and restarts Kolibri, they are now able to import, but only once.
• It is possible to import resources correctly from more than one channel in FF & Chrome.

Expected behavior

User needs to be able to import from more than one channel.

User-facing consequences

Impossibility to import content on IE11.

Errors and logs

Nothing visible in the console or network tab

Steps to reproduce

1. Open Kolibri in IE11 on Windows 7.
2. Import a resource from one channel from Studio
3. When the task is finished, try importing from another channel.

Context

• Kolibri version: 0.13.1b1
• Operating system: Windows 7
• Browser: IE11

I’ll install on Windows 10 and see if I can replicate on Edge.

cc @jonboiser @indirectlylit @lyw07