Improve speed of keyboard navigation through message list

[ramonsmits]

Problem

When browsing through the items in the listview SI is immediately loading the results and locks the listview.

Solution

It should use delayed event handling that only loads an item if it has been selected for more then for example 50 milliseconds. This allows to quickly scroll through the items with the keyboard without actually loading each item.

[HEskandari]

Sounds reasonable and the effort seems to be small.