Missing and wrong translations for German

[morpheus-87]

In the locales file for German there are missing these entries:

'yes': 'Yes',
'no': 'No'

in the section general.

In the section blocks there are some entries, that are not translated yet:

• for the image block the field upload_error should be corrected like this:

image: {
  'title': "Bild",
  'upload_error': "Es wurde ein Problem beim Upload festgestellt"
}

• for the heading block the field title should be corrected like this:

heading: {
  'title': 'Überschrift'
}