Fix relative paths in webhdfs.

This fixes relative paths in webhdfs by prepending
the users home dir whenever the path is relative.
Merge pull request #79 from jcrobak/webhdfs-fixes

Fix relative paths in webhdfs.
New luigi task status and graph visualiser (squashed for cleaner history, including commits by lallea, Anders Nyman and Uldis Barbans)
New hand-written layout engine more suited to directed acyclic graphs (like dependency graphs). Backend unit tests now use scheduler directly instead of RPC.
Killed old visualiser and fixed 2.7-dependent tests
Visualiser now fetched error traces from luigi. Failed nodes in graph are clickable for a traceback. Ships with mock data for testing UI in isolation
Added root path handler to redirect / to /static/visualiser/index.html
Merge pull request #80 from DavW/new-visualiser

New visualiser to display failing tasks and dependency graphs
Added recursive scan to setup.py to get round limitations is python's packaging
Changed to using relative paths for API calls. Useful if luigi entry-point root is changed to something other than /
Merge pull request #81 from spotify/freider/visualiser_relative_paths

Changed to using relative paths for API calls
Make MockFile a FileSystemTarget, add FileSystem.

Barebones "FileSystem" implementation for MockFile. Some semantics
don't 100% match hadoop fs, but this is a good start for testing.
Merge pull request #82 from jcrobak/mockfile-fs

Make MockFile a FileSystemTarget, add FileSystem.
Luigi parameters with defaults from config.

Allow default for a parameter to be specified in a config file.
The config is lazily loaded, so it's not evaluated on parsing
(useful in the case of calling LuigiConfigParser.add_config_path
to add additional configs at runtime).

Also,
* move config into its own module
* a test utility to override configs for testing.
Hive targets have customizable clients

- deprecated old methods
- no deprecate client
Merge pull request #83 from jcrobak/config-defaults

Luigi parameters with defaults from config.
Merge pull request #84 from rathboma/master

Now we pass the hive client to hive targets in the constructor
Classify tasks not found as 'UNKNOWN'

Fixes an exception we've been seeing in certain situations.
Merge pull request #85 from jcrobak/luigi-grep-fix-unknown

Classify tasks not found as 'UNKNOWN'
Support custom scheduler and RPC responder.  Factor out code smell in luigi.server.  Revive remote scheduler test.  Add test-generated files to .gitignore.