[xbuild] Reorganize xbuild targets/frameworks/bin data

They had been squashed into one single source directory
despite being installed into very different locations.

Made it easier to follow what's what by separating them
into:

* data: targets and data files for xbuild bin directory
* targets: misc pcl/web targets for extension directory
* frameworks: framework definitions
[xbuild] The 4.0 toolset is in the 4.5 directory
[xbuild] Do not allow running tests or installing exe w/4.0 profile

It's not a usable MSBuild 4.0 toolset, that's in the 4.5 profile directory.