Created a Boost.Python module interface in libcalamares.
Added a PythonJob wrapper and exposed it in the Python module.
Rename target calamareslib ==> calamares so in Python it's libcalamares.
Python-related classes in libcalamares that aren't exported as C++
symbols are now in a CalamaresPrivate namespace.
Import the libcalamares python module into every Python script before
running it.
Added Python error handling to PythonJobHelper.
Added some more testing code to dummypython module.

Added ViewManager.
Added dummy Settings class.
Added dummy plugin interface (UI plugins only).
Added dummy greeting plugin.
Added DLLEXPORT macros for UI plugin interface and plugins.