Bash Completion for cvmfs_server

This adds basic bash completion for `cvmfs_server`.
Additionally it moves the bash completion into the code-tree and installs it using CMake.

**CAUTION:** I rebased and adapted the branch (including Steve's [Pull Request](https://github.com/cvmfs/cvmfs/pull/342)) onto the current master. Please merge only this Pull Request to get everything.

**Note:** Pull Request is based on (and includes) Steve's prior [Pull Request](https://github.com/cvmfs/cvmfs/pull/342).