vimperator: declare escape keys explicitly per mode

Automated setup added in commit v1.4-61-g6d38d53c6c (2012-04-10)
[keys: replace omni-present escape keys] has been broken since commit
v1.7-126-ge1226a3e4c (2015-09-22) [dereference class definition includes].
Apply the intended effect as static data like other pages for simplicity.