Updated Gradle build file
Multiselection and nulling of adapter

1. In order to be able to tell which view is needed to be selected on
long click, we need actual position and not translated one (for
adapter). Then the responsibility of translating position is on client
code, where client should ask list view instead of list adapter for item
(because list view works with headers).
2. nulling adapter for a grid view would cause a NPE, so it had to be
handled