Allow closing of notifications by clicking on them

Adds a DoClick functions to notification icons made by notification/AddLegacy which changes the time left to display on the notification panel. Useful for when notifications might overlap GUI which is needs to be read or clicked on, but the entire panel is not clickable, which makes you less prone to accidentally close the panel.
Example: http://gyazo.com/15ebbcf7c769a127eee247ad49719c35.gif
Added SetMaterial to DImageButton

from DImage
Materials are now cached again

with DImageButton's inclusion of SetMaterial this now will work
SetMaterial updated
Merge pull request #617 from OzymandiasLlewellyn/patch-1

Allow closing of notifications by clicking on them