Implement filter subscription detection message's handler

[adbuker]

[adbuker]

resolved in adguard-windows/pull-requests/549 along with content-script/pull-requests/14 and core/pull-requests/1382
This is a test page

[adbuker]

How to test:

Test 1

1. Install AdGuard
2. Open the test page
3. Click the first link
4. Allow using the custom URL handler (a special request will appear)

Test 2

1. Install AdGuard
2. Open the test page
3. Click the second link
4. Allow using the custom URL handler (a special request will appear)

Expected: the dialog providing installation filter subscription appears