Move the flags classes out of GridOut and into a namespace of their own. This was...

Move the flags classes out of GridOut and into a namespace of their own. This was necessary since C++ does not allow us to explicitely specialize any of these classes, although the present use of this feature was accepted by gcc as an extension. We want to move to more closer C++ compliance, also in order to allow other compilers to translate the library.

git-svn-id: https://svn.dealii.org/trunk@4663 0785d39b-7218-0410-832d-ea1e28bc413d