Added UI for more complex tag filtering to files page
Refactored tag filtering in files page and added unit tests for filter logic
First somewhat working version of advanced tag filtering
Improved tag filtering

* Files are now correctly matched with NOT operator
* Logic is simplified
* Code redundancy has been reduced
Cleaned up tag filtering algorithm
Simplified tag search operator logic
Removed someTagsSelected value from tag filtering logic results

This logic should be left to controller because controller already gets a list
of selected tags.
Combined tag selected and operator properties into just operator property