Fix DB error when trying to tag a repository

Steps to reproduce: Go to a project settings, add tags, click on save changes

Observed behavior: Error 500

    PG::Error: ERROR:  column "taggings_count" does not exist
        LINE 1: UPDATE "tags" SET "taggings_count" = COALESCE("taggings_coun...

Ran rake acts_as_taggable_on_engine:install:migrations, removed the first migration that created the tags and taggings table, and added the rest.

• Closes #1512 (closed)
• Closes #1550 (closed)
• Closes https://github.com/gitlabhq/gitlabhq/issues/6867
• Closes https://github.com/gitlabhq/gitlabhq/issues/9194