remove build dir cleaning in the default build entrypoint

Background:

To give developers more control back about their build process, I decided because of #14, that the build directory should not get cleaned by default.
This should even be something that the docker image should not take care of at all. Close #14

Author: darkmattercoder

Diff for: entrypoint.sh

@@ -12,7 +12,6 @@ if [ "$1" = "build" ]; then
 		cd $APP_BUILDDIR
 		mkdir -p build
 		cd build
-		rm -rf *
 		qmake $ADDITIONAL_ARGS ..
 		make
 	fi