Redesigned Dependencies, completed ERD, implemented relation U.

[dimitri-yatsenko]

• foreign keys can now use aliased attributes (See Allow renaming the referencing attribute in a foreign key #206)
• ERD is now fully functional (See ERD: entity relationship diagram #7, ERD plotting support #82 )
• dj.ERD is now a standalone object for plotting dependencies
• dj.ERD now has a custom layout independent on pygraphviz
• simplified Fetch and removed slice indexing
• connection.dependencies is now a networkx.DiGraph
• removed text-based ERD
• Schema now has method spawn_missing_classes to explicitly bring missing classes into context; it should be invoked after all the other classes have been declared, e.g. at the end of the module.
• The _prepare callback has been removed. If a user relation has a contents property, it will be inserted only once at the time of the table declaration.
• All RelationalOperand classes have a copy constructor
• Implemented dj.U (previously proposed as dj.All in issue Implement the special relation dj.U  #112)
• AutoPopulate._populated_from has been renamed into poprel
• removed the demos directory
• added IPython notebook tutorial pages

[coveralls]

Coverage increased (+6.6%) to 82.212% when pulling fc2ed59 on dimitri-yatsenko:master into ee3e7dd on datajoint:master.

[coveralls]

Coverage increased (+6.6%) to 82.212% when pulling 1612b62 on dimitri-yatsenko:master into 8f70c67 on datajoint:master.

[coveralls]

Coverage increased (+10.4%) to 85.998% when pulling 0fce887 on dimitri-yatsenko:master into 8f70c67 on datajoint:master.

[fabiansinz]

Minor Comment: Maybe that should be renamed in 'Please cite us:'. Otherwise it sounds as if these are citations of datajoint.

[coveralls]

Coverage increased (+9.5%) to 85.078% when pulling 6be9bd8 on dimitri-yatsenko:master into 8f70c67 on datajoint:master.

[coveralls]

Coverage increased (+9.5%) to 85.101% when pulling 6be9bd8 on dimitri-yatsenko:master into 8f70c67 on datajoint:master.

[coveralls]

Coverage increased (+9.8%) to 85.391% when pulling 2540730 on dimitri-yatsenko:master into 8f70c67 on datajoint:master.

[coveralls]

Coverage increased (+10.0%) to 85.573% when pulling a5141a8 on dimitri-yatsenko:master into 8f70c67 on datajoint:master.

[coveralls]

Coverage increased (+10.2%) to 85.773% when pulling 6a6fc3c on dimitri-yatsenko:master into 8f70c67 on datajoint:master.

[coveralls]

Coverage increased (+10.0%) to 85.573% when pulling 486a5d6 on dimitri-yatsenko:master into 8f70c67 on datajoint:master.

[eywalker]

Looks good 😄