Implement simple functionality for relative HttpPath

[magicDGS]

We should implement a relative HttpPathto get parts of the Path (file name, directory name, etc), and also iterate over paths. This support should include:

• Add offsets field (int[]) for easier splitting the directory (as in other path implementations)
• isAbsolute() returning false for this paths
• toAbsolutePath() should return an absolute path sited on the root
• getFileName
• getParent
• getNameCount
• getName(int)
• subpath
• iterator - using getName(int)

In addition, this relative Paths should fail for constructing an URI (no relative paths there), with a meaningful error.