Change normal and visual mode behavior more strict

[gitusp]

It changes normal and visual mode behavior to cancel all the unassigned characters, to prevent accidentally input an unassigned(but exists in vim) character like "w" or "b". I thought no-op is better than accidental input. It does not cancel a key event if the key is pressed with ctrl or meta, not to mask Google Sheets' default shortcuts such as ⌘-F. It also adds explicit arrow key mappings to prevent canceling them because of the above change.