Make new location alerts location specific

[dadofsambonzuki]

Users should be able to set a radius of interest for alerts, with a default value of say 100km.

[bubelov]

Alerts are location specific, with a default radius of 100km, but this feature is a dead end, since it lacks flexibility. We can consider a "subscribe" button on the area screen though, which can allow the users to monitor changes for any specific set of countries or smaller communities