File properties: improve accessibility of the icon button

Neither the button nor the icon shown in the properties dialog had nay
name, which is a problem for accessibility as an assistive technology
thus doesn't have anything to present to the user apart from an unnamed
button or image -- which isn't particularly helpful.

Improve this in two ways:
* Add a description to the icon, either matching the file type display
  name of the icon, the fact it's a custom icon or conveying multiple
  files are selected and the icon is hence not very specific.
* Add a tooltip to the button hinting that it can be used to change
  the associated icon.

0 files changed, 0 insertions, 0 deletions