ALLJOYN-2471 SCons build option MSVC_VERSION defaults to 11.0

We no longer officially support MSVC 2008.  So we are changing
the default option to the most recent version of MSVC that we
support.

Change-Id: Ic760119ff66d6ca05bf101e09a7aec71f65bbce0
Simplify platform SConscript inclusions.

Change-Id: I8a5c6bfcabad6a063f2e8d389ea24e4602c831a6
ALLJOYN-1973: Make Android NDK usage more generic.

Remove implicit ties to specific versions of the Android NDK and use the NDK
to determine compiler/linker options.

Change-Id: Iba0ce2484dc7014f2a2857c9d0959334c6bf7f01