Keymap management through new filters

This is a proposal for a better Keymap management through new filters, particularly useful when porting previous userprefs to the newest Blender version, so we can clean the keymap more efficiently.

There are two main filters (can be both enabled at the same time or one by one, both are enabled by default):

• OFFICIAL KEYS: shows only the keys that are official to Blender, they have to come from the installation folder (C:\Program Files\Blender Foundation\Blender) to be considered official keys.
• ADDON KEYS: shows the keys that are coming specifically from addon scripts (either from "...\AppData\Roaming\Blender Foundation\Blender\2.80\scripts\addons" or from "C:\Program Files\Blender Foundation\Blender\2.80\scripts\addons").

And then, there are default sub-filters , applicable to both "Official" and "Addon" (enabled by default):

• Default Keys: keys that haven't been touched by the user.
• Changed Keys: keys the user has changed.
• New Keys: keys the user has added.

And finally, there are special sub-filters , used to detect and single out specific errors (disabled by default). When clicked, they disable the rest of the other sub-filters (they are Solo Mode if you will).

• Deleted Keys: keys the user has deleted (with the cross) from the Official or Addon database. Maybe could have a restore button next to it as a way to restore only that one, and not the entire editor keymap (disappears from the list if restored).
• Conflict Keys: shows all operators that share the same shortcut within the same space, mode or editor, that will lead to one of them taking priority and occlude the other.
• Ghost Keys: keys that do nothing. Often unnoticeable, they can be a new operator miswritten by the user, but most likely an obsolete key after an API break occured for that functionality. Example: when the operator "view3d.select_border" became "view3d.select_box", it still remained as a ghost key: "VIEW3D_OT_select_border", before I removed it after spotting it.