Add python3-dev to the edxapp dependencies.
Add python3-dev to the edxapp dependencies.

This is because some of the edxapp python libraries need to compile C
Extensions for python.  This will install headers needed for that
compilation to succeed in python 3.

arbrandes/edx-configuration,arbrandes/edx-configuration,mitodl/configuration,stvstnfrd/configuration,EDUlib/configuration,stvstnfrd/configuration,EDUlib/configuration,appsembler/configuration,stvstnfrd/configuration,appsembler/configuration,EDUlib/configuration,edx/configuration,edx/configuration,arbrandes/edx-configuration,mitodl/configuration,appsembler/configuration,stvstnfrd/configuration,edx/configuration,arbrandes/edx-configuration,appsembler/configuration,mitodl/configuration,stvstnfrd/configuration,mitodl/configuration,arbrandes/edx-configuration,EDUlib/configuration,edx/configuration,EDUlib/configuration