Clld

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Upgraded leaflet and leaflet-provider plugin.

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Bugfixes:
- https://github.com/clld/clld/issues/108
- https://github.com/clld/clld/issues/109

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fixing bugs in CLDF export.

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Backwards incompatible changes:

- clld does no longer provide support for imeji metadata files.
- The test utilities have been refactored. For typical clld apps,
which used `TestWithEnv` and `TestWithApp` with `__setup_db__==False`
this should not change anything.

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Fixing bugs in new CLDF export.

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Updated support for creating CLDF downloads.