Log Message:
biology/molsketch: update to 0.7.1

Unfortunately, there were quite some unintended bugs in the last version (some
of them older than that, however), which are being addressed by this version.
Saving files and re-opening might have sometimes led to crashes due to
inconsistencies in the drawing's data. This should now be fixed in, if not all
at least most of the cases.
Likewise, copying, cutting, and pasting is more robust now.
The last version prematurely updated some code leading to incompatibilities
with older versions of Qt (especially pre-5.14). These older versions should
now work again; support for Qt 4, on the other hand is completely removed, as
it is doubtful whether that still worked anyway.
Translations should now really work throughout Molsketch (currently supported
languages: Chinese, English, German, Greek).
Finally, for Windows, an installer is provided, which will download from a
repository hosted at github.