Make English the source language of the interface text

Every tr() source string in the code and the forms is now the English
text, and French is a translation (qet_fr.ts) like the other languages.
Generated, not hand-edited: master ef795a21e5 converted by
qet-en-source (harness 4c4ddc9).

3144 messages get an English source, 665 already had one, 0 left French; 8 shared-wording pairs disambiguated.
C++: 2904 literals in 233 files. Forms: 809 strings in 65 files. All 34 .ts files re-keyed; qet_fr.ts filled.
lupdate check: PASS. What each of 38 languages shows, old vs new: same 118266, English instead of French 38433, comment fallback 51, differences 0.

sources/titleblock/templatescollection.cpp

@@ -148,7 +148,7 @@ QString TitleBlockTemplatesProjectCollection::title() const
 		if (project_title.isEmpty()) {
 			final_title = QString(
 				tr(
-					"Cartouches du projet sans titre (id %1)",
+					"Title blocks of untitled project (id %1)",
 					"collection title when the parent project has an empty title -- %1 is the project internal id"
 				)
 			);
@@ -156,7 +156,7 @@ QString TitleBlockTemplatesProjectCollection::title() const
 		} else {
 			final_title = QString(
 				tr(
-					"Cartouches du projet \"%1\"",
+					"Title blocks of project \"%1\"",
 					"collection title when the project has a suitable title -- %1 is the project title"
 				)
 			);