Fix handling of arrays in the REST API filter

The REST API accepts filter parameters in the URL, which can contain multiple values for one property. The internal handling in the used query builder checks for arrays of filter values, to create "IN" expressions in the resulting SQL query. However, if an array is recognized, the term "IN" will be selected as the operator, but the value array will not be handled correctly. This leads to a syntax error like the following: "Errormesage: [Syntax Error] line 0, col 78: Error: Expected Doctrine\ORM\Query\Lexer::T_OPEN_PARENTHESIS, got ':cleared'".
Adding parentheses, as well as one parameter key for each value in the array and replacing all these keys with their values later fixes this error.

Conflicts:
	engine/Shopware/Components/Model/QueryBuilder.php
Automatically preselect first customer group in price group management dialog

Currently discounts, which are associated to a price group, are lazy-loaded, when the user selects a customer group. Since the save action for price groups simply overwrites the data stored in the database with the data received from the client, this behavior leads to the deletion of associated discounts, if the user only alters the name of a price group without "lazy-loading" the discounts before he clicks the save button. The automatic preselection of the first customer group ensures, that the discounts are always been loaded, when the user triggers the save action.
Use extended article name in add article popup
Hide buy now button if laststock flag is set and article is out of stock
Improve customer search

The filter string can now contain multiple filter tokens separated by spaces. The where-clauses for each token are combined by logical AND.
Fix banner slider

Fixes the problem, that a link for a banner image is only clickable outside of the navigation slider container.
Increase interval for backend login check
Add smarty modifier prettynumber
Add article number to user questions form
Add possibility to retrieve logged in user in smarty templates