Editors: Add an option to enable/disable the camel case navigation.

The user can change the setting in Option->Text Editor->Behavior.

Reviewer's note: We do have alternative ways to disable camel-case
operations through the shortcuts. Nevertheless, this particular option
has been quite requested since it disables every camel-case based
operation at once. In addition, it seems that the shortcuts are still
not "visible" or "expected" for many users.

Change-Id: I04364760f4b43123fd9e06c0c52ba9e6a5688e2c
Merge-request: 392
Reviewed-on: http://codereview.qt-project.org/6419


Reviewed-by: Leandro T. C. Melo <leandro.melo@nokia.com>
Sanity-Review: Qt Sanity Bot <qt_sanity_bot@ovi.com>