Significant reorganization of the CFE core directory
and header file structure.

All modules become separate subdirectories under fsw/modules.

Additionally, the interfaces to CFE core (public and internal)
are also separated into modules.

CMake "interface libraries" and related constructs are used to
manage the include paths to all the separate modules.

Updates the application developer guide to describe the directory
structure and file naming conventions

This updates the cppcheck static analysis rule to run via a script
which takes into account the new directory structure.

Oddly this reported new (valid) issues in FSW code which have also
been corrected.

Notably the wrapper script also contains a special provision to
run static analysis on TIME only with SERVER mode enabled.  The
default logic of cppcheck would run all combos and it is not valid
to have both of these defined.

The userguide build needs to include fsw/inc from all modules

Create a separate "core_internal.h" header file for prototypes
that were only intended for CFE core use.

Fix #972, reorganize directory structure

Certain operations in the recent baseline were dependent on a
recent version of CMake.  In particular object libraries cannot
be used in the intended way in the older versions.  This adds
workarounds for those cases.

Tested against CMake versions 3.5.1, 3.10.2, and 3.16.3.