[NGO Admin][Import Observers] The form doesn't reset automatically

[danniel]

Steps to Reproduce:

1. Log into the NGO Admin with an admin account
2. Go to Observers > Monitoring Observers
3. Press Import observers list
4. Select a file, then press Import list
5. You will the the success or failure message
6. Press again Import observers list
7. Select the same file
8. The Import list button remains disabled

Expected behaviour:

The Import observers list form should reset itself after each submission.