Import: Create new entries and update existing rows.

Allows keep db_match_field into insert using a new
argument $keep_match_field of import method.
This argument is false for a compatibility purposes.
Bug: Import breaks if a row contains a apostrophe into the db_match_field
Import: Is more safer transform to UTF-8 (default is set by config.php)
When $keep_match_field=true rows without db_match_field must be ignored.
Show how match_field will be used according to importation method.
Merge pull request #92 from jorix/i-utf8

Import: Is more safer transform to UTF-8 (default is set by config.php)
Merge pull request #91 from jorix/i-bug-apostrohe

Bug: Import breaks if a row contains a apostrophe into the db_match_field
Merge pull request #90 from jorix/i-addUpdate

Import: Create new entries and update existing rows.
DBWrap: Force SQL_MODE=''

Force `SQL_MODE=''` since there are pages that fails if `'STRICT_TRANS_TABLES'` is used.

eg `manage providers.php` fails when:
 * creates a new provider without "Processing time":
 `error 1366: Incorrect integer value: '' for column 'offset_order_close'`
 * goes to list products of a provider:
 `error 1292: Incorrect date value: '0'` at `CALL get products_detail`