Don't require restart to apply settings

[Tom Beckmann]

When changing one of the listed keys below in dconf, you need to restart in order to apply them. It would be better for the shell plug to give direct visual response, so applying changes done to slingshot instantly.

Non applied keys:
- show-category-filter
- rows
- columns
- icon-size

[Andrea Basso (voluntatefaber)]

Now rows and columns are updated on the fly.
I don't think show-category-filter is of any importance, it shouldn't even be in the shell plug, if we're ever gonna add Slingshot to it. But if it were required, it wouldn't be a problem to make update without restart.
Icon-size doens't update on the fly yet because that option isn't available yet, or at least, it's unusable. While you can actually change icon size, that's the only thing you change, the space that every app receives in the grid doesn't change, which makes this option pointless. When it's properly added, as part of https://blueprints.launchpad.net/slingshot/+spec/better-scaling , it'll updates on the fly.
For this reasons, I'm marking this as fixed.