Subscription indicator is not correct when notification level is 'on mention'

Description

When on mention notification level is set, subscription indicator is wrong, because it says that I'm subscribed to an issue / merge request, while it is not true.

Currently, in order to explicitly subscribe to an issue / merge request, I need to click "notification" bar twice, and then refresh a page to see if this actually works.

Solution

When I'm not subscribed by default, subscription indicator should say that I'm not subscribed.

/cc @smcgivern @victorwu