accounting: respect case convention in previous period date fields names

At and From should not be title cased in "Previous Period At/From Date"
message.

bt5/erp5_accounting/SkinTemplateItem/portal_skins/erp5_accounting/AccountModule_viewBalanceSheetReportDialog/your_at_date_previous_period.xml

@@ -90,7 +90,7 @@
                 </item>
                 <item>
                     <key> <string>title</string> </key>
-                    <value> <string>Previous Period At Date</string> </value>
+                    <value> <string>Previous Period at Date</string> </value>
                 </item>
               </dictionary>
             </value>

bt5/erp5_accounting/SkinTemplateItem/portal_skins/erp5_accounting/AccountModule_viewBalanceSheetReportDialog/your_from_date_previous_period.xml

@@ -85,7 +85,7 @@
                 </item>
                 <item>
                     <key> <string>title</string> </key>
-                    <value> <string>Previous Period From Date</string> </value>
+                    <value> <string>Previous Period from Date</string> </value>
                 </item>
               </dictionary>
             </value>

bt5/erp5_accounting/SkinTemplateItem/portal_skins/erp5_accounting/AccountModule_viewProfitAndLossReportDialog/your_at_date_previous_period.xml

@@ -90,7 +90,7 @@
                 </item>
                 <item>
                     <key> <string>title</string> </key>
-                    <value> <string>Previous Period At Date</string> </value>
+                    <value> <string>Previous Period at Date</string> </value>
                 </item>
               </dictionary>
             </value>

bt5/erp5_accounting/SkinTemplateItem/portal_skins/erp5_accounting/AccountModule_viewProfitAndLossReportDialog/your_from_date_previous_period.xml

@@ -85,7 +85,7 @@
                 </item>
                 <item>
                     <key> <string>title</string> </key>
-                    <value> <string>Previous Period From Date</string> </value>
+                    <value> <string>Previous Period from Date</string> </value>
                 </item>
               </dictionary>
             </value>

bt5/erp5_l10n_fr/MessageTranslationTemplateItem/fr/erp5_ui/translation.po

@@ -9244,10 +9244,10 @@ msgstr "Page précédente"
 msgid "Previous Period"
 msgstr "Exercice N-1"
 
-msgid "Previous Period At Date"
+msgid "Previous Period at Date"
 msgstr "Date de fin période précédente"
 
-msgid "Previous Period From Date"
+msgid "Previous Period from Date"
 msgstr "Date de début période précédente"
 
 msgid "Previous bank statement balance does not match reconciled balance at previous bank statement date"