Replace placeholder implementation by Qt5.2 placeholder. Fix issue 76.
Merge pull request #89 from Schlumpf/qt52-placeholder

Replace placeholder implementation by Qt5.2 placeholder.
Made undo/redo disablable/enablable
Added a clear button to the filter widget
Fixed a bug of Esc not cancelling name/status changes
Made username and status message labels copyable
Moved some of context menus to stack
Removed unused variable, made some formatting fixes
Updated build instructions
Merge remote-tracking branch 'upstream/master'

Conflicts:
	projectfiles/QtCreator/TOX-Qt-GUI.pro