Added static_list option

Added a new option: static_list. It allows filtering by some predefined terms, that do not change during searches. 
The list can be classical (like filter lists) or it can be a 'oneorless' list. The oneorless list allows, as the name says, only one ore no selection. Therefore, if one value is selected, when a new selection is made, the first value will e deselected.   
(E.g. list of languages that is always constant, so users can always know what other languages are available)