Summary:
Ref T7789. This implements:
- A new table to store the `<objectHash, filePHID>` relationship between Git LFS files and Phabricator file objects.
- A basic response to `batch` commands, which return actions for a list of files.
Test Plan:
Ran `git lfs push origin master`, got a little further than previously:
```
epriestley@orbital ~/dev/scratch/poemslocal $ git lfs push origin master
Git LFS: (2 of 1 files) 174.24 KB / 87.12 KB
Git LFS operation "upload/b7e0aeb82a03d627c6aa5fc1bbfd454b6789d9d9affc8607d40168fa18cf6c69" is not supported by this server.
Git LFS operation "upload/b7e0aeb82a03d627c6aa5fc1bbfd454b6789d9d9affc8607d40168fa18cf6c69" is not supported by this server.
```
With `GIT_TRACE=1`, this shows the batch part of the API going through.
Reviewers: chad
Reviewed By: chad
Maniphest Tasks: T7789
Differential Revision: https://secure.phabricator.com/D15489
