Correcting the name of the Tohoku earthquake

BUR #30957 has been approved by @nonamethanks.

create alias 2011_sendai_earthquake_and_tsunami -> 2011_tohoku_earthquake_and_tsunami

The earthquake is actually known as Tohoku earthquake because it affects the entire eastern provinces of Japan, so naming it "Sendai earthquake" is misleading especially since it is called as "Tohoku earthquake" everywhere else.

It was named that way after Wikipedia's article, which was then renamed four days after the earthquake (and the tag) happened.

The bulk update request #30957 (forum #305249) has been approved by @nonamethanks.