Add RegisterAttribute for cleaner stack traces

AddToBackstack Flag not respected fix.

Fixes issue #295

MvvmCross initialization support for WakefulBroadcastReceiver.

Fixes issue #292

Conflicts:
	MvvmCross.Droid.Support.Design/MvvmCross.Droid.Support.Design.csproj
	MvvmCross.Droid.Support.Design/packages.config
	MvvmCross.Droid.Support.V14.Preference/MvvmCross.Droid.Support.V14.Preference.csproj
	MvvmCross.Droid.Support.V14.Preference/packages.config
	MvvmCross.Droid.Support.V17.Leanback/MvvmCross.Droid.Support.V17.Leanback.csproj
	MvvmCross.Droid.Support.V17.Leanback/packages.config
	MvvmCross.Droid.Support.V4/MvvmCross.Droid.Support.V4.csproj
	MvvmCross.Droid.Support.V4/packages.config
	MvvmCross.Droid.Support.V7.AppCompat/MvvmCross.Droid.Support.V7.AppCompat.csproj
	MvvmCross.Droid.Support.V7.AppCompat/MvxCachingFragmentCompatActivity.cs
	MvvmCross.Droid.Support.V7.AppCompat/packages.config
	MvvmCross.Droid.Support.V7.Preference/MvvmCross.Droid.Support.V7.Preference.csproj
	MvvmCross.Droid.Support.V7.Preference/packages.config
	MvvmCross.Droid.Support.V7.RecyclerView/MvvmCross.Droid.Support.V7.RecyclerView.csproj
	MvvmCross.Droid.Support.V7.RecyclerView/packages.config

Issue #289 back stack fix

AddToBackStack flag has not been respected by ShowFragment method - when Fragment was not available in cache.
Issue #289 fix

Make IMvxRecyclerViewHolder methods virtual, in class MvxRecyclerViewHolder 

Get latest changes

Update to latest support packages

Clear bindings on ViewHolders when the RecyclerView is detached.

Keep WeakReferences of all ViewHolders created by the adapter.  When the
associated RecyclerView is detached from the window we clear the bindings.
Note that this does not Dispose of the ViewHolder since the Adapter doesn't
really manage the lifetime of the ViewHolder and there is no callback for
when the ViewHolder is destroyed.

Without this we leak target bindings.

Fixes https://github.com/MvvmCross/MvvmCross/issues/1379

Rotating with Fragments fails with saved states