update NKJWebViewProgress; fixes progress bar in iOS 8
update default bookmarks
greatly improve how error messages are displayed. lots of code cleanup here.
fix progress bar not appearing if first url load happens too quick
catch some more error types that should not display
fix issue where browser stops if the user tried to go back/foward or to homepage or to a bookmark while a current page is still loading resources. (related to #53)
Allow using mirrors to download Tor when building the dependency.

May provide some relief to users in locations which block torproject.org.

Fixes #48.