Update Esri.ArcGISRuntime.Toolkit.csproj

Updated reference to 10.2.3
Converted Toolkit to a universal project
Delete unused project file
Updated output folders
Updated output and extension sdk manifests
Updated feature data form fields for Windows Phone
Fixed error border placement for windows phone feature data form.
Added error message box to windows store feature data form.
Adjusted margin alignment for widows store feature data form error message.
Updated VSIX packaging script for WP8.1 + general tweaks to manifests
Merge branch 'v.next' of https://github.com/Esri/arcgis-toolkit-dotnet into v.next
Update README.md
Update README.md
Update README.md
Fixed vsix file include settings
Updated DependsOn version
Merge pull request #46 from Esri/v.next

Merge v10.2.3 into master