Default to substring filtering, add option to go back to fuzzy filtering

By default we now search for substrings; you can search for multiple substrings
by separating them with spaces. Add a config option gui.filterMode that can be
set to 'fuzzy' to switch back to the previous behavior.

pkg/gui/types/context.go

@@ -102,10 +102,10 @@ type IFilterableContext interface {
 	IListPanelState
 	ISearchHistoryContext
 
-	SetFilter(string)
+	SetFilter(string, bool)
 	GetFilter() string
 	ClearFilter()
-	ReApplyFilter()
+	ReApplyFilter(bool)
 	IsFiltering() bool
 	IsFilterableContext()
 }