Updated db connectors

Now you can use chained methods.
Like this $db->setQuery()->execute();
Updated setup script

Added db connector choice.
Added some slash config params.
Demo datas are now separated and optionnaly installed.
Removed old db_slashcms.sql
Merge branch 'master' of https://github.com/wakdev/slash-cms

Conflicts:
	core/common/class/db/mysqli/connector.php
	setup/SlSetup.php
Fixed : Database setup bug introduced since last setup update
Updated README.md
Merge branch 'master' of https://github.com/wakdev/slash-cms

Conflicts:
	setup/sql/slashcms.sql
Moved responsive images rewrite to sl_images
Added responsive images support to sl_articles/sla_articles
Fixed attachments display in sl_articles
Reverse README.md
Moved responsive images rewrite to sl_images
Added responsive images support to sl_articles/sla_articles
Fixed attachments display in sl_articles
Added high density screens support
Fixed attachments images preview in back office
Merge pull request #65 from lowki/master

Moved responsive images rewrite to sl_images