Original feedback
moves test to correct place
CommandParser renamed to CommandFactory.
Renames submit method to getCommand
Renames view command method to read command to match domain language.
Fixes shameful bug in wall ordering.

Bug caused by rounding error from conversion from long to int for compareTo ordering.

Bug is now exhibited by delaying a second between wall posts in cucumber scenarios.
Moves posting into PostCommand.execute().
Moves reading into ReadCommand.execute().
Moves following into FollowCommand.execute().
Moves wall into WallCommand.execute().
Removed unnecessary constructor params
Removes getUserName from Command interface, left it in place where required.
Makes sorting of posts more terse.
Introduces a new aggregate for the data access layer, which all commands talk through.
Folds in the manufacture of walls into the data repository.
Reorganises test, to isolate those still using a cast and inspecting the command internals.
Optimises imports.
Removes size() and anyMatch() in favour of external assertion over contents and length.
Adds test for user repo.
Renames InMemoryDataRepo to DataRepositoryImpl
Moves Subscriptions into an internal class for tracking other user a user follows
Removes the WallFactory class and moves the ordering of all timelines for a wall into the datarepo
Adds test for data repository impl that includes verified test for the ordering bug when posts are within a second of each other in nano seconds