refactor(admin/translations): merge domains

[Davidmattei]

Q	A
Bug fix?	n
New feature?	n
BC breaks?	n
Deprecations?	n
Fixed tickets?	n
Documentation?	n

Merged emsco-user.en.yml into emsco-core and translated in NL & FR
Merged emsco-environment.en.yml into emsco-core and translated in NL & FR
Merged emsco-component.en.yml into emsco-core and translated in NL & FR
Merged emsco-contenttype.en.yml into emsco-core and translated in NL & FR
Merged emsco-forms.en.yml into emsco-core and translated in NL & FR
Merged emsco-twigs.en.yml into emsco-core and translated in NL & FR

Renamed the emsco-mimetypes domain to ems-mimetypes, making mimetypes translatable on the front-end as well.

Stats about the translations:

nl
  emsco-core: used 950, unused 0, new 0, untranslated 0
  validators: used 18, unused 0, new 0, untranslated 0
  ems-mimetypes: used 63, unused 0, new 0, untranslated 0

fr
  emsco-core: used 950, unused 0, new 0, untranslated 0
  validators: used 18, unused 0, new 0, untranslated 0
  ems-mimetypes: used 63, unused 0, new 0, untranslated 0

en
  emsco-core: used 950, unused 0, new 0, untranslated 0
  validators: used 18, unused 0, new 0, untranslated 0
  ems-mimetypes: used 63, unused 0, new 0, untranslated 0