Added passing in build flags to the go build command

May be used by the revel run, build, package, test or debug commands to send specific flags
to "go build" like -ldflags -extldflags=-fno-PIC which would allow you to resolve issue #631 in the booking app on some machines

Signed-off-by: NotZippy <notzippy@gmail.com>
Merge pull request #766 from notzippy/add_build_args

Added passing in build flags to the go build command