Allow owners paths to be arbitrarily long and add storage for display paths

Summary:
Depends on D19182. Ref T11015. This changes path from text255 to longtext because paths may be arbitrarily long.

It adds pathDisplay to prepare for display paths and storage paths having different values. For now, pathDisplay is copied from path and always has the same value.

Test Plan:

• Ran migration, checked database for sanity (all pathDisplay and path values identical).
• Added new paths, saw pathDisplay and path get the same values.
• Added an unreasonably enormous path with far more than 255 characters.

Maniphest Tasks: T11015

Differential Revision: https://secure.phabricator.com/D19183