Merge branch 'release-0.2.3' into development
Improve the edit student id dialog in Windows.

Fixes #67. The text field of the combobox did not get the focus. The
reason was probably a faulty implementation of showPopup() in Windows.
Now showPopup is not called to prevent this from happening.
Two small fixes to the user manual.

- The "-h" option is no longer in eyegrade.eyegrade.

- The package "python-numpy" seems not to be installed in some
versions of Ubuntu when python-opencv is installed. A dependency
problem in the Ubuntu package of python-opencv?
Merge branch 'development' of github.com:jfisteus/eyegrade into development
Update changelog and version number for release 0.2.4.
Merge branch 'release-0.2.4'