Honour Locale.accesskey_localization in translate view

[mathjazz]

We use Locale.accesskey_localization flag to disable pretranslation of accesskeys for selected locales.

We should honour the flag also in the translate view: instead of generating candidate keys, we should prefill the accesskey value with the value in the source string.

[flodolo]

we should prefill the accesskey value with the value in the source string

I assume we should do that only when the user starts filling one of the other fields, otherwise it'll be a nightmare to move between strings without translating (string has changed = confirmation to leave the current string).