Assume "about:blank" as an empty URL.

- Closes #1539
Fix debug output with Qt 5.4

Qt 5.4 outputs a malformed "QSslSocket: cannot resolve SSLv2_client_method ("
message on first SSL connection and it breaks all terminal output.
WebView: Fix zoom shortcuts with +/-/0 on numeric block
ProxyStyle: Set tabbar alignment to left

Closes #1547
AdBlock: Fix hiding iframes that have completely blocked contents

Closes #1552
AdBlock: Use display:block when hiding blocked iframes

visibility:hidden leaves empty space in page
Allow closing Download Manager and Browsing Library with CTRL+w