kconfig: Reorganize kconfig interfaces into subfolders.

For each kconfig interface flavour move all files belonging to the flavour into a separate
subfolder.

Split the kconfig main makefile: Only targets for the line-oriented program and
special targets remain in the main file, move all interface specific targets into
their respective makefile.

Tested with libgtk 2.24, Qt 4.8.4, libncurses 5.9