Assign temperature manually to multiple measurements

[MartinKrater]

If temperature wasn´t recorded during a measurement, I´d like to assign the same temperature to multiple measurments in order to calculate YM. Currently, it´s only possible one by one.

[paulmueller]

I implemented this in 87a119f.

You can find this feature in the "Bulk Action" menu. Could you please test it thoroughly (try to break things) and let me know whether it works as expected?

Development version download for Windows:
https://ci.appveyor.com/project/paulmueller/shapeout2/builds/36405730/artifacts

Todo:

• update documentation
• write test functions