Added triple click on TextInput to select text.

Added triple click on TextInput to select text.

Once it gets a double click, it'll start to monitor any other extra
click for a short duration. Once it is detected, the monitor stops
watching and all text is selected. It only works when selectByMouse
property is set, just like double click selecting current word.

Also added a test case that simulates clicking at the same point
and triggering the triple click, and another one that contemplates
movement of mouse between the second and the third click. Also test
timing between clicks.

Task-number: QTBUG-21038

Change-Id: I139f7ece2107f5dbfcba1836afb27aaa9b24fc57
Merge-request: 6
Reviewed-by: Andrew den Exter <andrew.den-exter@nokia.com>
Reviewed-on: http://codereview.qt-project.org/5761
Reviewed-by: Qt Sanity Bot <qt_sanity_bot@ovi.com>