Bug 31286: Implementation of bridge, proxy, and firewall settings in about:preferences#connection

This patch adds a new about:preferences#connection page which allows
modifying bridge, proxy, and firewall settings from within Tor Browser.
All of the functionality present in tor-launcher's Network
Configuration panel is present:

 - Setting built-in bridges
 - Requesting bridges from BridgeDB via moat
 - Using user-provided bridges
 - Configuring SOCKS4, SOCKS5, and HTTP/HTTPS proxies
 - Setting firewall ports
 - Viewing and Copying Tor's logs
 - The Networking Settings in General preferences has been removed

Bug 40774: Update about:preferences page to match new UI designs