Fix some Bugsense-reported exceptions.
Update to latest version of Android Studio.
Clean up ExploreActivity.

This should hopefully fix this Bugsense-reported exception:

The application's PagerAdapter changed the adapter's contents without
calling PagerAdapter#notifyDataSetChanged! Expected adapter item count:
1, found: 3 Pager id: com.gh4a:id/pager Pager class: class
android.support.v4.view.ViewPager Problematic adapter: class
com.gh4a.activities.ExploreActivity$ThisPageAdapter
Exclude ourself when redirecting to browser.

As our browse filter matches most Github links, Octodroid is (confusing)
also included in the disambiguation list when choosing the 'Open in
browser' option inside Octodroid. Fix that by using our own chooser,
just like we already did when we couldn't open links our intent filter
matched on.
Merge pull request #210 from maniac103/for-upstream

Some fixes for Bugsense reported bugs