PO Filter: allow msgctxt to be included in TU note

[Chase Tingley]

Discussion here.

PO msgctxt information is used to disambiguate contexts where the same string may need to be translated differently. Existing behavior will look for a special magic word in the msgctxt data to determine the TU ID.

Although the PO spec indicates that a msgctxt value shouldn't be a full comment, in some cases the context data provides useful information to the translator to help inform translation. We can enable this by adding an option that would include the msgctxt value in the TU note along with any other comment information.

[Chase Tingley]

Fix Issue #584: PO Filter: Add option to include msgctxt in segment note

→ <<cset 97f407b67f94>>