Added notes on the build

Basically pointed out you need QT 4.8 minimum and that use newer
libs if they exist from Windows except for libusb (0.1.12 required)
Less right-click on Activity list

.. group by and field chooser now appear on the
popupMenu in the sidebar.
Fix sidebar groupby column names error

The visual headings are not reset when the view is reset, for
example after startup. This means the wrong columns are offered
on the activity popup menu for group by.

The resetView() function needed to call columnsChanged() to get
the visual headings reset.
Explicit memory allocation for CLucene

.. clutching at straws, but more explicit type declaration and usage to
try and resolve Win7 64bit issues with cross-compiled 32bit binaries.