- the strange construction of Helper and treating it as a singleton
can be factored out into a separate singleton-handling instance()
function. The Helper should never be destroyed.
- Take the Python wrapper for GlobalStorage out of the GlobalStorage.h
header and add it to PythonHelper instead, saving some work in
all the cases that only GS is interesting, not the Python bits.
Use dict methods, in particular d.get(k, v), to retrieve
the pretty_name() function (or None if it isn't there).
Using getattr() on a dict will not return values in the
dict.
Rename PythonJobHelper ==> CalamaresPython::Helper.
Add QVariant to boost::python::object conversion functions.
Rename some constants in the libcalamares Python API.
