Piccolo-admin

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Modified the release process, so it works on GitHub (courtesy olliglorioso).

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Added Finnish translations (courtesy olliglorioso).

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Added translations, to make the UI more accessible in a variety of languages
(thanks to sinisaos for helping with this).

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``TableConfig`` now has a ``hooks`` argument - so custom logic can be run when
a row is added / deleted / modified. Thanks to Anton-Karpenko for suggesting
this feature.

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The WYSIWYG editor we use for ``rich_text_columns`` has been modified, so the
user can now create HTML headings. Thanks to tigerline86 for suggesting this
feature and sinisaos for implementing it.

Rows can now be bulk modified - for example, if you have 100 blog posts which
need converting to ``draft=False``, it can now be easily done using the
Piccolo Admin GUI in a single operation (courtesy sinisaos).

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More sandbox fixes.

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