#98 Changes not taken into account

[Nicolas Weeger]

To reproduce:

• launch Gridarta
• open a map
• select an item
• in the "object editor", change some value
• click on another square/item

=> changed value is lost

[Nicolas Weeger]

Work around: after changing a value, switch to 'events' or 'apparance' tab, and the change is correctly taken into account.