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/dataBase/ui/summaryquerywidget.ui

@@ -35,7 +35,7 @@
       <item row="0" column="0">
        <widget class="QLabel" name="label">
         <property name="text">
-         <string>Informations disponibles</string>
+         <string>Available information</string>
         </property>
         <property name="alignment">
          <set>Qt::AlignCenter</set>
@@ -48,7 +48,7 @@
       <item row="0" column="2">
        <widget class="QLabel" name="label_2">
         <property name="text">
-         <string>Information à afficher</string>
+         <string>Information to display</string>
         </property>
         <property name="alignment">
          <set>Qt::AlignCenter</set>
@@ -154,7 +154,7 @@
      <item>
       <widget class="QCheckBox" name="m_edit_sql_query_cb">
        <property name="text">
-        <string>Requête SQL :</string>
+        <string>SQL request  :</string>
        </property>
       </widget>
      </item>