Maven build

Fixes the maven build by moving metadata.xml to a directory of its own.

I also moved the maven-runonce scripts since their use was impractical as they would unnecessarily load the pom.xml when run, being in the same directory

I took steps so that the Ant build should still run

PS: like the other pull request I submitted today, https://github.com/tschneidereit/SwiftSuspenders/pull/81, the commits exhibit full-file diffs even though the files seem identical except for the specific changes I made. I offer my apologies as I cannot figure how to fix that.