Add userscripts to Extensions module when using "Subscribe" button

### STR:
1) Go to https://testcases.agrd.dev
2) Find two tescases for userscripts ("Userscripts" and "Userscripts: GM API v4 tests")
3) Click on Subscribe in front of each of them

### Expected result:
Subscriptions are defined as userscripts and added to Extensions module.

### Actual result:
Subscriptions are added to Filters module.

Screenshots: