"Fixed" the invisible dialog error, as in #209

The problem was that if you center a dialog wider/taller than the screen, it will overflow. Since albow draws widgets by openGL, it won't accept negative coordinates for the bottom left corner. my hotfix minimizes these coordinates.

This is not a complete solution, and some of the filters, for example, will still be out of the screen. At least now we see what's going on.
Merge pull request #329
Added: ALT+Mouseover shows full NBT tags for TileEntities.

Without ALT, shows tags minus the "Items" tag.
Submodule pymclevel updated.

Submodule pymclevel:
    > 3dcd449 - Added: Block rotation for several new blocks.
    > d02d446 - Static defs for blocks > 115