Gradle build script

Here is my proposal for a build.gradle script.
It is probably not the best way to make multiple .jar files but I have tested many times with consistent success so at least it works.
Dependencies are managed using gradle. I didn't like the idea of putting them in libs folder, e.g. If I `git clone` I should be able to `gradlew build` without manually adding files.

Also included in this pull request:
Updated forge to latest recommended version.
I made some changes to OreDictionary calls as the latest forge changed some things. Please check it works as expected, I have not properly tested my changes.
Bumped up the version of the gradle wrapper while I was at it.
gradlew.bat included for Windows users.
Item names fixed. For `tile.projectred.illumination.lamp` I could not work out how to know when to add `.inv` onto it so just made it go up to 31 instead.

I deleted the build.xml file, should be pure gradle now.