* Any work that might use Qt needs to happen on the UI thread, so when
running a python script on the python thread we need to invoke across.
We wrap the main ICaptureContext interface to block invoke onto the UI
for any function calls that aren't just returning internal data.
* Added a couple of utility macros to help with the conversion. lit() is
paired with tr() for untranslated text.
* QFormatStr is more explicitly for non-textual formatting strings.
* Both are just #define'd to QStringLiteral()
baldurk