added ability for SALR to set image tooltip based on image filename

I have added the ability for SALR to set an image's tooltip based on the file name. In addition, I gave some basic options for user control, including:
* the option to leave emoticon tooltips alone (Default on)
* the option to leave tooltips alone when already set (Default on)
* the option to strip the file extension off the tooltip (Default on)

The new master setting will default to off, so people won't be wondering why their images are suddenly displaying weird text when they mouse over them.

Because files for emoticons are a bit scattered, and I've seen non-emoticon images hosted on the somethingawful domain, the paths to their general locations are hard coded, and will need to be updated should the forums software ever change where emoticons are stored.