Ender Bucket: Fix the non-flowing water/lava bug + other fluid handling stuff.

Some fixes and clean-ups to the fluid handling code in the Ender Bucket code.
We now check if we have the vanilla water or lava source blocks, and
convert them to the flowing variant before trying to place them.
Also fixed some other fluid handling bugs, where we didn't properly check
if the fluids are identical, which allowed for duplication in some cases.
Move every package and class to a shorter package path + other renames.

So basically remove the .mods.minecraft from the package path.
Also renamed and reorganized some packages and divided some classes into
smaller classes (mostly Reference classes).
Ender Pearl: Don't drop the pearls in Creative mode (workaround).

The workaround is because for some reason I can't change the stackSize
at all in creative mode, even if changing the item to a different type!
It will always get reverted to the size it was originally.
Add a "teleport self" mode to the Ender Bow. Add tp sounds/particles to items.

Added separate icons for the "tp self" mode. The Bow's mode can be toggled
with a hotkey, which is by default the middle mouse button.

Also, some items were missing teleport sounds and/or particles.
They now have them, in both the source and destination sides.
The Bow (or the arrows to be more precise) however doesn't currently
have particles, due to the way that part of the code doesn't get executed
on the client side.
Update/improve the Gradle build script stuff.