v3.1 updates to PCL 158, WP8, Mvx 3.1.1.-beta2, and iOS 7 layout as needed

**Done**

- changed all PCLs to Profile 158 (4.5, SL5, WP8, Store, Xam iOS/Droid) instead of PCL Profile 104
- upgraded all Mvx packages to 3.1.1.-beta2 versions
- converted all Windows Phone projects to target Windows Phone 8 instead of 7.1
- added iOS 7 layout check to all iOS projects as needed (tried to guess the right places anyway) :)
- updated readme with new blogspot link and to explain why the first 43 videos are profile 104, not 158 like the repo code is now. (***May want to add a similar note to the blogspot video index so new people are not confused***).

**Known Issues**

-  `N-22-AndroidDemo`: updated PCL, Mvx binaries.  Please confirm this is working as expected as I guessed on binary needs and did not try it on a Mac as it was originally intended.
- `N-26-Fraggle`: fix Android build failure (see fragment issue below).
- `N-27-Ninja`: not updated. Please use the Ninja Coder add-in to update all the non-nuget Lib references in this project.
- `N-40-Maps`: fix Android build failure (see fragment issue below).
- `N-41-Maps`: fix Android build failure (see fragment issue below).
- `Z-MacOnly`: not updated. Please review this folder to update or delete it.
- This repo is large (200MB) and chooses to include the nuget dlls inside of each N+1.  Because each N+1 was updated with the latest 3.1.1.-beta2 dlls, all of the old v3.0.x dlls are no longer used.  At some point we may want to investigate "safe" git ways to purge these "deleted" dll files. TBD if it really makes any significant difference.

**Android Fragment Issue**

All of the Android build failures above seem to be related to a reference to: 

`Android.Support.V4.*` types of things.

Once that is resolved, the Droid-related projects that are mentioned above should be fixed so that they will build.

Potentially related [Xamarin bug 15205](https://bugzilla.xamarin.com/show_bug.cgi?id=15205) filed by @slodge and [SO question](http://stackoverflow.com/questions/19125901/mvvmcross-trying-to-use-fragments-and-latest-support-lib-results-in-linking-pr).