Feature: Exclude Patterns in .cvmfsdirtab

This adds exclude patterns to the *.cvmfsdirtab*. The syntax looks like this:
```
/Project/Versions
! 1.*
! 2.??
! 2.0
```
This *.cvmfsdirtab* would create nested catalogs for each directory in **/Project/Versions** except for all 1.x versions, 2.xx versions (exactly two digits in the minor version) and 2.0.

Additionally it contains an integration test for the exclusion patterns.