core, mod_l10n: add timezone support.

(cherry picked from commit e073558a924c52300eb684b8c4aefffcaccbb3ab)

Conflicts:
	rebar.config
	src/db/z_db_pgsql.erl
	src/zotonic.app.src
core: fix qdate github url.

(cherry picked from commit 9760d1868f250f9091574f1a2c227beeddc5faf8)

Conflicts:
	rebar.config