Added PopupLayout view

PopupLayout added.
Android chart component fixed.
Merge branch 'master' of github.com:XForms/Xamarin-Forms-Labs

Conflicts:

src/Xamarin.Forms.Labs/Plugins/Charting/Xamarin.Forms.Labs.Charting.Droi
d/Controls/ChartSurface.cs
Android ExtendedScrollView
workaround selected item by @badstorm  close #236
Merge pull request #250 from dirric/master

autocomplete code cleanup
close ##249
update nuget spec beta4
Update Helper.
Merge pull request #253 from saramgsilva/master

Update Helper.
Merge pull request #252 from jguertl/master

Android ExtendedScrollView
Numerous fixes for WP Charting
Included new screenshot for correct WP chart
screenshot
Merge remote-tracking branch 'upstream/master'
Merge pull request #254 from Snorvisable/master

Numerous fixes for WP Charting
Merge branch 'master' of https://github.com/XForms/Xamarin-Forms-Labs