[i18n] microbit-fs errors, particularly "There is no storage space left"

[microbit-matt-hillsdon]

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As noted on #146 the error when the file system is too large is passed directly to the user from microbit-fs.

We should find a way to translate this, e.g. introduce error codes into the library and map to translatable (and perhaps more verbose) messages in the app.

V2 has the same issue.