Improve check for existing HWMs near where users are making a new one

[lprivette]

It seems like when you are going to add a HWM site that the map should show all existing HWMs site nearby. I believe if you start adding a site it will say a site is nearby if it is some distance like within a 100 ft of that site. But, it just seems like you could look the existing sites and then choose whether one of those is close enough to the one you want to add. I just added a HWM near a know site and it was way better than it was.