Intercept abp:subscribe and subscribe.adblockplus.org URLs

[ameshkov]

https://issues.adblockplus.org/ticket/2208

Look at these filters:
https://adblockplus.org/subscriptions

You should first compare the subscription URL you've got with the subscription URLs of the filters you have. If it matches any you should enable this filter in AG.

If no match found we should offer user to import the rules to his "User Filter"