Update MCP mappings and add Maven POM for faster decompile-free building

Updates to the last MCP 7.26a mappings in Forge 6.6.2 (had to do this to get it to compile), and adds a new Maven pom.xml as discussed on IRC for quick and easy building without MCP or decompilation:

    Install Maven 3
    mvn initialize -P -built
    mvn package

On my system, builds Tinker's Construct in 5 seconds:

[INFO] ------------------------------------------------------------------------
[INFO] BUILD SUCCESS
[INFO] ------------------------------------------------------------------------
[INFO] Total time: 4.980s
[INFO] Finished at: Sat Mar 09 14:27:22 PST 2013
[INFO] Final Memory: 25M/345M
[INFO] ------------------------------------------------------------------------