Add folder generation for the solution.

This commits adds the folder generation i requested in issue #36.

There are 2 different Generation Types (**Action**) available:
* **PerModule** - generates one folder per module found
* **MirrorFilesystem** - generates one folder foreach folder one the Filesystem. 

I also added one option:
* **SkipLast** (Skipp the Last Folder / Module)

This is an **opt-in** and you need to enable it in your **Module.xml**:
For **PerModule**
```
  <GenerateSolutionFolders>
    <Action>PerModule</Action>
    <SkipLast>false</SkipLast>
  </GenerateSolutionFolders>
```

For **MirrorFilesystem**
```
  <GenerateSolutionFolders>
    <Action>MirrorFilesystem</Action>
    <SkipLast>true</SkipLast>
  </GenerateSolutionFolders>
```

I prefer the MirrorFilesystem option.