This adds the core infrastructure needed to support binary file patching

when applying review request diffs using rbt patch.
rbtools.diffs.patches.BinaryFilePatch represents binary files in the

diff, and can lazily load their content as-needed.
rbtools.diffs.patcher.Patcher now has several methods to apply binary

files in various ways. They can be overridden by SCM-specific patchers

to perform file operations as necessary.
rbtools.diffs.patches.PatchResult will now track which binary files

were applied (or failed).
The rbt patch command has been updated to:

Fetch binary file metadata from diff and commit resources.
Pass binary files to Patch instances.
Report binary file application results
Add the new --no-binary option, which skips patching binary files.

Subsequent changes will add support for individual SCM systems.

Ran unit tests.
Used this in conjunction with later changes to actually apply patches

  that include binary files.