Reset MessageList::seen_id in mail_reader_message_seen_cb()

Otherwise invalid source ID is used in the call of g_source_remove()
when is tried to remove "pending" auto-mark-as-seen timeout callback.
It can show a runtime warning on a console too.
Updated Russian translation
Updated Russian translation
tests: rename test m4 to a nice name

The new m4 also fixes srcdir != builddir issue
tests: Continue button was renamed to 'Next'
tests: initial setup: find windows by roleName


Headerbar is now uses in initial setup wizard, so the name of window changes on moving to a different page
tests: initial setup: rewrite Next/Continue button detection
tests: don't check that Skip Lookup button is hidden due to bug 726539
Bug #727888 - Wrap the Location label in a reminder dialog
Bug #727967 - Undo/Redo text is not displayed in menus
Bug #684425 - Do not pass NULL text to gtk_entry_set_text()
Updated Slovenian translation
Newly created folders always marked as having subfolders

This corrects, a bit, a regression caused by commit b0106cc8, reported at
https://bugzilla.gnome.org/show_bug.cgi?id=722698#c13