zotonic-tpl-mode: autocomplete closing tag soup tags.

Yell out to @arjan for the feat request! ;c)
Also adjusts indentation as you type...
(cherry picked from commit e45f3311d62fccdc89c1a0b444ee6c6da985d2a8)
zotonic-tpl-mode: improved auto close tag.

Works for tempalte tags too, for those that begin with ``{% end``.
(cherry picked from commit f2514c0fb1e21aa0534e381a27febd47c4a2f563)