Fixes #981 Add Japanese translation

[yuryu]

Description of proposed changes

Adding the Japanese locale files.

Related issue(s)

Fixes #981

Testing

Change the locale setting to Japanese and check translations.

[jameshadfield]

Thanks Emma!

This looks great but there are a some strings missing (e.g. all the sidebar.json strings are still in english). If you run npm run diff-lang -- ja then you'll be able to track which keys are missing etc 😄 Here's the current output:

npm run diff-lang -- ja

JA: comparing sidebar.json against the English translation
        Following keys need to be added:
                "Show confidence intervals"
        Following keys are identical to the English version & may need to be translated:
                "Dataset"
                "Date Range"
                "Color By"
                "Tree Options"
                "Layout"
                "rectangular"
                "radial"
                "unrooted"
                "clock"
                "Branch Length"
                "time"
                "divergence"
                "Branch Labels"
                "Search Strains"
                "Second Tree"
                "Map Options"
                "Geographic resolution"
                "Animation Speed"
                "Loop animation"
                "Animate cumulative history"
                "Panel Options"
                "Show tree"
                "Show map"
                "Show entropy"
                "Language"
                "Slow"
                "Medium"
                "Fast"
                "full"
                "grid"
JA: comparing translation.json against the English translation
        Following keys need to be added:
                "A full list of sequence authors is available via the TSV files below"
        Following keys are present but should be removed as they are no longer used:
                "A full list of sequence authors is available via the TSV files below."
        Following keys are identical to the English version & may need to be translated:
                "Built with"
                "Click to zoom out to parent clade"
                "Gaps"

[yuryu]

Thanks for reviewing! I added translations for these literals. Also, I needed to adjust the original text for "more" because numbers need to come after "more" in Japanese.

[jameshadfield]

Brill! Thanks for updating the other languages with the necessary changes 😄

Never thought translations like this would happen, this is really cool 💯