Disambiguate "%u folder"

[jeremypw]

Running io.elementary.files-update-po gives the following warning

xgettext: warning: msgid '%u folder' is used without plural and with plural.
                   src/View/Widgets/OverlayBar.vala:180: Here is the occurrence without plural.
                   src/Dialogs/PropertiesWindow.vala:1283: Here is the occurrence with plural.
                   Workaround: If the msgid is a sentence, change the wording of the sentence; otherwise, use contexts for disambiguation.

This fixes that.

[jeremypw]

On reflection this might cause issues with languages that use the singular form for other numbers so returning to draft.

[jeremypw]

Using ngettext in both places should be better.

[tintou]

I think that there is still the issue of the whole sentence being made out of concatenation not working for all languages I think

[jeremypw]

@tintou Agreed. I may as well try and fix that here as well.

[jeremypw]

Keeping everything translatable into all languages is something of a challenge given the variablity of the status messages. I have tried to minimise the different msgids while maintaining flexibility for the translators. Fairly extensive comments are added. I assume that translators are familiar with positional arguments.

We may have to more radically change the layout of the status message in English to fully achieve translatability but I have kept fairly close to the existing layout for now.

[jeremypw]

@ryonakano Thanks for the review - sorry about the careless mistakes. Hopefully now fixed.

[jeremypw]

@ryonakano Sorry, I thought I applied your suggestion last time. Something must have gone wrong. I have applied it this time for sure.