External database import user-interface tweaks

Small improvements to the shared database import functionality.
* Since sync and import are the more common options with a shared supplier, put them first.
* Move supplier selection button to top right (next to title)
* Use icon to indicate unit_quantity
* When a category is preselected, import shows no dialog (for mass importing)
* Other small user-interface cleanups
![shareddb_ui](https://f.cloud.github.com/assets/503804/2207983/86fadbf4-997a-11e3-9edf-574450e5e032.png)