ci: add `set -x` in scripts/release-version.sh and remove it from scripts/deploy-new-stable-version.sh for debugging

- Add details in README on how to correctly install npm dependencies
- Modifiy protractor.config.js to solve issue with the error message "unknown error: session deleted because of page crash" (Solution found in https://stackoverflow.com/questions/53902507/unknown-error-session-deleted-because-of-page-crash-from-unknown-error-cannot)

Release version 4.15.0

See merge request !133

Resolve "Cloisons > Générer une PAB: vider les champs"

Closes #516

See merge request !126

Refs #516

Refs #516

# Conflicts:
#   jalhyd_branch

refs #516

test(e2e): check calculation works in generated PAB from 'standard fish ladder' example (walls calculator)

refs #516

test(e2e): check computed parameter initial value is not null with "empty fields on calculator creation" option

refs #516

Resolve "CI: affiner la gestion du cache"

Closes #526

See merge request !130

Resolve "Courbe de remous:  Crash de l'application sur données erronées"

Closes #532

See merge request !132

refs #516

refs #516

fix: graph crash in backwater curves calculator when embankment has a high value and calculation does not converge

refs #532

refs #516

refs #516

refs #516

refs #526

Resolve "Sections: non convergence du calcul du tirant d'eau critique"

Closes #528

See merge request !125

Draft: Resolve "Cloisons: il manque l'aide contextuelle pour les lois de débit"

Closes #529

See merge request !127

Resolve "Transfert du site de production sur OVH"

Closes #505

See merge request !128

Resolve "Plantage des e2e sur les exemples (le retour)"

Closes #531

See merge request !131

add sleep()s

refs #531

refs #516

fix: empty field 'number of falls" of 'generate fish ladder' dialog when 'enable empty fields on new calculator' option is set

refs #516