Changed default yank/paste binds.

Also added additional tab switching binds.
gt/gT move forwards/backwards, and [n]gt will go to a specific Nth tab.
J/K move forwards/backwards, and [n]J/K will go to N tabs forwards or
backwards.
Added key binding for tabhistory

Makes it quick to enter this mode.

RATIONALE: some sites (I'm looking at you, reddit) seem to create lots of
history items for each page load that make the normal back/forward
bindings near useless.