Build system cleanup

configure.ac:
	Indent/alignment
	Silent building aka AM_SILENT_RULES([yes])
	Remove non-used --with-default-plugins=PLUGINS
	Since cairo-xlib-xrender is a mandatory dependency, always build annotate
	Remove non-used --with-max-desktops

kde/window-decorator-kde4/Makefile.am:
	Indent/alignment

plugins/Makefile.am:
	Indent/alignment
	Remove leftover @LIBPNG_CFLAGS@ from AM_CPPFLAGS
	Always build annotate, so remove if ANNOTATE_PLUGIN/fi, $(libannotate_module)
	Remove leftover $(libfs_module)

src/Makefile.am
	Indent/alignment