Fix #264 - better error messages on file loading error

e2e/load-malformed-files.e2e-spec.ts

e2e/session/session-bad-syntax.json

e2e/session/session-empty-modules-list.json

e2e/session/session-format-too-old.json

e2e/session/session-missing-info.json

e2e/sidenav.po.ts

protractor.conf.js

...ts/dialog-load-session/dialog-load-session.component.html

...ts/dialog-load-session/dialog-load-session.component.scss

...ents/dialog-load-session/dialog-load-session.component.ts

src/locale/messages.en.json

src/locale/messages.fr.json