Geyser fixes + 1 addition

It was brought to my attention that when using :flash() on a Geyser.Label you could not click on the label while the flash is occurring. I have resolved this by having the Label:setClickCallback() function store the callback and args as it would if the callback were set at creation time, and then having the label created for :flash() inherit the callback of its parent. 

I also added Geyser.Miniconsole:clear() as there is currently no function to run a clearWindow against geyser miniconsoles.