fix onSelected event for markers with custom view

[yonahforst]

addresses #436, parts of #553

Problem: when using markers with a custom subview, didSelectAnnotation does not get triggered on tap events, unless you press on the outside edge of the marker (outside the subview but inside the marker)

Solution: 'marker-press' events manually call selectAnnotation on the marker's mapview

[lelandrichardson]

Thank you!

[leonardogutierrezh]

this creates an issue when you have multiple markers close together, the callout box jumps between the different markers

[switz]

Can this be hidden behind a flag? I believe it's causing multiple callouts to open on iOS when they're nearby.