Changed queries to avoid trashed files.

Also changed a method name.
Added syncability to DirectoryEntry.getDirectory.

This includes support for creation/retrieval of a directory at a path.  Drive doesn't support paths, so recursive traversal is necessary.

Also generalized directory creation (previously, only the creation of the syncable app directory existed).
Also assigned an error callback to a method in cases when it didn't exist.
Also added tests.
Generalized creation of root and app directories.

These special directories previously had their own functions; now they're created and retrieved using the same functions as all other directories.
Added creation/updating of a file at a path.

Drive doesn't support paths, so recursive traversal is necessary.

Also removed some unnecessary function and callback parameters.
Also added a test.