Add callback for changed items

[ovidiuch]

Need

We need to know whenever item positions change in order to persist them with a server setup. When making server updates, we are only interested in the items that changed their position in the last interaction.

Deliverables

• [x] A changed callback after
  • The grid was resized
  • An item was dropped
  • An item was resized
• [x] This callback should receive a list of items that had either their position (x, y) or size (w, h) changed

  Solution

  Prerequisites

• [required dependency for identifying the problem, scope and then solution for this issue]

  TODO

• [logical step in completing this story]

  Files

• [path to a file involved in this story]

  Notes

• [peculiar aspect relevant this story]

  ETA [0-2]p

[ovidiuch]

CR @valentinzberea @aismail

[ovidiuch]

Move something here to see the visual effect http://ubervu.github.io/grid/

[valentinzberea]

Finished review