Bug 32609: (follow-up) enhance Makefile.PL

Bug 32609: (follow-up) enhance Makefile.PL

This patch adds a new target to the Makefile which gets
called as the first step of the "all" target. This means
that CSS and JS files get compiled every time "make" is
called.

(Note: Since the "install" target depends on "all", it will
 be re-run at install time.)

Signed-off-by: Martin Renvoize <martin.renvoize@ptfs-europe.com>
Signed-off-by: Tomas Cohen Arazi <tomascohen@theke.io>
(cherry picked from commit 550bb87ecb619dedb5d42a82cde46506e141c26f)
Signed-off-by: Martin Renvoize <martin.renvoize@ptfs-europe.com>