Issue #1808 Escape unsupported special characters in search queries

[Wedds]

This PR is related to issue #1808.

The user is aware of 'Special expressions' of the Global Search and characters, which function as operators in a query. But since not all the symbols are declared as supported, it would be convenient to automatically escape them to avoid search failures and side-effects. From now, all the special symbols of the QueryString query, which are not described as an operator for Global Search, are escaped automatically.