Snap to grid and fixed size increments

Allow users to decide if they would like cards to snap to grids and allow fixed size increments.

This isn't ready yet and requires the following (I just wanted somewhere to make public notes):

* If server restarts whilst user is connected to board we loose socket details
  * This also causes an exception and kills process
  * Catch exception
  * Then create a 'something has gone wrong, automatically refresh board event
* Tidy up board creation form 
  * Help details
* Decide whether to allow changes to this from admin
  * If so there will need to be a warning when switching from a grid to free-form (things won't align)

Apart from card creation none of the sizes/positions are checked when saving to database. I feel this is fair although we need to have a discussion about this. Maybe later we could have a fix positions/sizes function when switching.