NEW multistage Dockerfile make images 5-10% smaller

[JonBendtsen]

NEW multistage Dockerfile make images 5-10% smaller
Applying this PR will use a multistage Dockerfile that reduces image size between 5 and 10%.

Warning:
v15 did not build - could be it needs some adjustments, but do we really need it?

Tested in develop with hurl and clicking around.

----- Run hurl test on APIs ---
INFO: 1. Running tests (API,GUI,public) that do not require authentication
Success api/00_explorer.hurl (1 request(s) in 28 ms)
Success api/00_foobar.hurl (1 request(s) in 29 ms)
Success api/status/00_status.hurl (1 request(s) in 31 ms)
Success public/payment/00_payment_newpayment.hurl (1 request(s) in 31 ms)
Success gui/00_HOME.hurl (1 request(s) in 32 ms)
Success public/onlinesign/00_onlinesign_newonlinesign.hurl (1 request(s) in 38 ms)
Success api/login/00_login_POST.hurl (1 request(s) in 1040 ms)
Success api/login/00_login_GET.hurl (1 request(s) in 1041 ms)
--------------------------------------------------------------------------------
Executed files:    8
Executed requests: 8 (7.7/s)
Succeeded files:   8 (100.0%)
Failed files:      0 (0.0%)
Duration:          1044 ms (0h:0m:1s:44ms)

INFO: Using existing DOLAPIKEY.
INFO: 2.a. Running API tests that do require authentication
Success api/status/10_status.hurl (1 request(s) in 23 ms)
Success api/setup/10_setup_company.hurl (1 request(s) in 40 ms)
Success api/setup/10_setup_conf.hurl (1 request(s) in 49 ms)
Success api/users/10_groups.hurl (15 request(s) in 331 ms)
Success api/eventattendees/10_eventattendees.hurl (19 request(s) in 297 ms)
Success api/users/10_users.hurl (17 request(s) in 382 ms)
Success api/emailtemplates/10_emailtemplates.hurl (23 request(s) in 414 ms)
Success api/setup/10_setup_dictionary_countries.hurl (18 request(s) in 442 ms)
Success api/mailings/10_mailings.hurl (34 request(s) in 555 ms)
Success api/setup/10_setup_modules.hurl (13 request(s) in 600 ms)
Success api/setup/10_setup_dictionary_countries_load_region_state.hurl (28 request(s) in 878 ms)
Success api/compta/facture/10_facture.hurl (20 request(s) in 1733 ms)
--------------------------------------------------------------------------------
Executed files:    12
Executed requests: 190 (109.1/s)
Succeeded files:   12 (100.0%)
Failed files:      0 (0.0%)
Duration:          1741 ms (0h:0m:1s:741ms)

Success gui/save_login_cookie.hurl (2 request(s) in 129 ms)
--------------------------------------------------------------------------------
Executed files:    1
Executed requests: 2 (15.4/s)
Succeeded files:   1 (100.0%)
Failed files:      0 (0.0%)
Duration:          130 ms (0h:0m:0s:130ms)

INFO: 2.b. Running GUI tests that do require authentication
Success gui/10_HOME.hurl (1 request(s) in 58 ms)
Success gui/eventorganization/10_conferenceorbooth_list.hurl (1 request(s) in 100 ms)
Success gui/admin/10_mails_templates.hurl (1 request(s) in 123 ms)
Success gui/comm/mailing/10_mailing.hurl (1 request(s) in 135 ms)
Success gui/eventorganization/10_eventorganization.hurl (4 request(s) in 337 ms)
Success gui/projet/10_projet_element.hurl (15 request(s) in 589 ms)
--------------------------------------------------------------------------------
Executed files:    6
Executed requests: 23 (38.9/s)
Succeeded files:   6 (100.0%)
Failed files:      0 (0.0%)
Duration:          591 ms (0h:0m:0s:591ms)