Improvements for Keymap menu

The keymap menu deserves a polish IMO. Here are some ideas:

• keep the top menu (Name/Key-Binding-Search Bar) sticky, so we dont have to go all the way up if we want to change those settings

• improve the search function, which seems a bit inconsistent. For example, if I search for the X/Y/Z axis (in this case in the Transform Modal map), it wont find them no matter what I write ("X Axis, "Y Axis, "Z Axis" in the name/key binding, or my custom keymap in the Key-binding category)

Here is another example with an operator bound to Double A: