Plugins: Don't exclude allowed plugins from available plugins list

This fixes issue that the allowed plugin (enabled by user) would
disappear from the all plugins list (in preferences) after failing
to load on startup.
Building: Use system QtFtp module when available with Qt5

See #1503
Remove hdi.de from list to force SSLv3
AdBlock: Use one cache for all subscriptions

Added new class AdBlockMatcher that holds the cache of
all subscriptions with rules.
This moves the matching logic from AdBlockSubscription into
separate class.
It also fixes issue that CSS exception rules weren't able to
affect rules from different subscription.
Remove live.com from list to force SSLv3
Adjust default font sizes
Cleanup displayed build configuration flags in qupzilla:config

Removed KDE Integration and WebGL. Both flags don't have much use now.
KDE Integration only enables KWallet plugin building (and only when
KWallet-dev is available).
WebGL is now enabled by default by any recent QtWebKit versions.

Also show Win7API flag only on Windows.
Settings: Allow nesting instances without breaking groups

Closes #1511
Mac: Fix Preferences... action in application menu

Make sure the Configuration Information action won't be
detected as "Preferences..." action.

Also use native shortcut for fullscreen (Ctrl+Meta+F)

Closes #1332
Fix build with Qt 4.7
1.8.4 is latest stable release
1.8.4 is current stable now
Fix build on Mac with Qt4

QKeySequence::FullScreen was only added in Qt5

Closes #1513
LineEdit: Fix slow text selection with mouse

Regression from 2c0582b9a1967d424d2645c72e1fdb803aed13de
ChinaList is deprecated and has been replaced by Easylist China

Fixes #1516
Preferences: Prevent opening more than one window
Use open() instead of exec() in all dialogs

Avoid blocking exec().

Closes #1515
Mac: Open new window when clicking on Dock icon

Closes #1517
OpenSearchEngine: Use Json class instead QScriptEngine to parse suggestions
Fixed "Open blank tab" on new tab option on OS/2