Add "About Privacy" menu item to open privacy FAQ

Fixes issue #128.
Merge pull request #134 from guilherme-pg/issue-128

Add "About Privacy" menu item to open privacy FAQ
Use text change events to save nickname.

This is a possible workaround for issue #112.
Merge pull request #135 from guilherme-pg/issue-112

Use text change events to save nickname.
Rename "About Privacy" menu item to "About MozStumbler"
Remove legal notice dialog
Zoom out initial map position and auto-size the location circle to fit
Avoid unregistering an already unregistered receiver
Handle null map
Merge pull request #137 from cpeterso/cpeterso/about

Rename "About Privacy" menu item to "About MozStumbler"
Merge pull request #138 from cpeterso/cpeterso/map-ux

Add some map UX tweaks and error handling