added a simple switch for AND/OR filtering in 'Advanced Filtering'
move CSS style of filter switch to screen.css
clearer and simpler UI layout for switch
rewrote template html and css rule for buttons
toggle states are now saved with cookies
revised KeywordFilter for structure
fixed: multiple pinned keyword filters are not colored correctly
revised and added test case for toggle switch
Merge pull request #54 from sh1r0/and_or_filter_switch

added a simple switch for AND/OR filtering in 'Advanced Filtering'