Move Up button handling into BaseFragment

.../src/org/briarproject/android/blogs/BasePostFragment.java

...roid/src/org/briarproject/android/blogs/BlogFragment.java

...roid/src/org/briarproject/android/blogs/FeedFragment.java

...id/src/org/briarproject/android/blogs/ReblogFragment.java

...org/briarproject/android/contact/ContactListFragment.java

...src/org/briarproject/android/forum/ForumListFragment.java

...d/src/org/briarproject/android/fragment/BaseFragment.java

...org/briarproject/android/sharing/BaseMessageFragment.java

...briarproject/android/sharing/ContactSelectorFragment.java