Summary: add ColumnFamilyHandleDeletionStarted listener which can be called when user deletes handler.

Test Plan: ./listener_test

Reviewers: yiwu, IslamAbdelRahman, sdong, andrewkr

Reviewed By: andrewkr

Subscribers: andrewkr, dhruba, leveldb

Differential Revision: https://reviews.facebook.net/D60717