BUG: Avoid unneeded copy of resource bytes

Modify qSlicerCoreApplication::[un]registerResource to use the
QByteArray's constData() rather than mutable data() in order to avoid an
unnecessary detach of the internally shared data. (Our usage does not
require a mutable pointer at any time.)
BUG: Fix qrcc.py operation on Windows

Change qrcc.py to use a temporary file to receive the raw binary rcc
data on Windows, in order to work around what appears to be a bug in rcc
where it is performing line ending (LF -> CRLF) conversion when writing
to stdout, resulting in corrupt data which causes Qt to crash when
trying to load the resources.

See also https://bugreports.qt-project.org/browse/QTBUG-39422, r23297.
BUG: Reenable Extension Wizard module

The previous commit should resolve the issue that was causing the
Extension Wizard module to crash Slicer; therefore, revert r23297,
making it enabled again.