[DB][FEATURE] Add ISO 639-1 keys to sys_language

The language handling of records in TYPO3
is solely based on UIDs of the sys_language DB table,
but no reference to the real language used.

The ISO 639-1 defines the language identifiers
(ISO language code) completely (182 entries).

If the real language key was needed before in
TYPO3, one could install static_info_tables
which takes a field ("static_lang_isocode") in the
various places of the TYPO3 Core and fetches
the isocode via separate SQL-Queries.

The change introduces the ISO language
two-letter-keys natively in the core in order to
1. use less SQL queries in FE and BE if
static_info_tables was installed
2. remove hard coded dependencies of
EXT:static_info_tables
3. and always ensure that the core
includes the ISO code

Additionally one can now use the
$TSFE->sys_language_isocode all the time for
working with the ISO code instead of the
UID parameter, meaning that isocode can now be
set with a TypoScript parameter as well.

A Migration Wizard moves values put in the old
DB field (which is a UID reference to
static_languages) to the new DB field "language_isocode".

The old field is deprecated to use without the
new properly filled field "language_isocode".

In TYPO3 CMS 8 the static_lang_isocode field
will be removed within the CMS core (but could
still be included in static_info_tables).

Releases: master
Resolves: #61542
Change-Id: Ia017af52af354ac204ffac11635d99df120b029a
Reviewed-on: http://review.typo3.org/32884
Reviewed-by: Markus Klein <klein.t3@reelworx.at>
Tested-by: Markus Klein <klein.t3@reelworx.at>
Reviewed-by: Georg Ringer <georg.ringer@gmail.com>
Tested-by: Georg Ringer <georg.ringer@gmail.com>