build: ignore build/install_manifest.txt

Signed-off-by: Luka Perkov <luka.perkov@sartura.hr>
include: move headers to include/freenetconfd

Signed-off-by: Luka Perkov <luka.perkov@sartura.hr>
include: move installed header files to include/

Signed-off-by: Luka Perkov <luka.perkov@sartura.hr>
project: add missing copyright headers

While at it also fix some other small typos.

Signed-off-by: Luka Perkov <luka.perkov@sartura.hr>