add Makefile to build libplsdk.so

This creates a single shared libplsdk.so library with all
the other PLSDK libraries statically linked into it
(libpldraw, libplepaper, libplinput).
fast-builder/Makefile: add `plsdk' to the list of libraries
Makefile: add -ldl to linker flags
android-ndk/Application.mk: add plottest
move Makefile to fastbuilder/libplsdk/Makefile

This Makefile is especially for the fast-builder, and this
then allows it to be packaged into the source archive.