Objects directly in world

Can now specify location in a b2 world where initial objects should be
placed.
Bug fix

Density of filled with liquid
Merge pull request #252 from jonvitale/master

Update
Added functionality into Table step. Added title drop down and ability
for student to add and delete rows and columns.
Merge branch 'master' of https://github.com/WISE-Community/WISE-VLE
Updated constraint bug

using tag map constraints now
Three bugs fixed (container, feedback, builder)

Containers were not being displayed.
Feedback expressions can now have parentheses.
The builder (original) now clears properly.
Merge branch 'master' of https://github.com/WISE-Community/WISE-VLE into authoringv2