Add ability to run configurable "preupdate" and "postupdate" shell scripts during image file writing.

Preupdate runs before replacing the .png, postupdate runs after. Both wait for completion before continuing, so scripts should be fast, or fork into the background themselves if appropriate. The image file name is provided as an argument.

Expected use-cases:
-Run optipng or similar in preupdate
-Upload to webserver or flush caches in postupdate

I'm sure there are others too. :)
Added "blockIronScaffold" texture to IC2
Update renderdata/ic2-texture.txt

Added "blockIronScaffold"
Merge pull request #15 from Blast0r/master

Added "Iron Scaffold" to ic2-textures and renderdata
Merge pull request #11 from Maeyanie/master

Add ability to run configurable shell scripts before/after writing tile images
Remove Java 7 specific code in Maeyanie's PR
Switch to more structured configuration settings for image update exits
Prevent overlapping file updates on JsonFile update
Start Pam's Mods Support
Add Pam's HC Candle mod
Add Pam's HC Cherry mod
Add Pam's HC Chilipepper Mod
Add Pam's HC Corn Mod
Add Pam's HC Cotton mod
Add Pam's HC Cucumber mod
Add Pam's HC Grape mod
Add Pam's HC Lemon mod
Add Pam's HC Lettuce mod
Add Pam's HC Onion mod
Add Pam's HC Peanut mod