Prepare UI for revealing contacts

This changes the visibility of some methods, removes unnecessary
abstractions and fixes static import of GroupId constant.

briar-android/src/org/briarproject/android/contactselection/BaseSelectableContactHolder.java

@@ -0,0 +1,58 @@
+package org.briarproject.android.contactselection;
+
+import android.support.annotation.UiThread;
+import android.view.View;
+import android.widget.CheckBox;
+import android.widget.TextView;
+
+import org.briarproject.R;
+import org.briarproject.android.contact.BaseContactListAdapter.OnContactClickListener;
+import org.briarproject.android.contact.ContactItemViewHolder;
+import org.briarproject.api.nullsafety.NotNullByDefault;
+import org.jetbrains.annotations.Nullable;
+
+import static org.briarproject.android.util.AndroidUtils.GREY_OUT;
+
+@UiThread
+@NotNullByDefault
+public class BaseSelectableContactHolder<I extends SelectableContactItem>
+		extends ContactItemViewHolder<I> {
+
+	private final CheckBox checkBox;
+	protected final TextView info;
+
+	public BaseSelectableContactHolder(View v) {
+		super(v);
+		checkBox = (CheckBox) v.findViewById(R.id.checkBox);
+		info = (TextView) v.findViewById(R.id.infoView);
+	}
+
+	@Override
+	protected void bind(I item, @Nullable
+			OnContactClickListener<I> listener) {
+		super.bind(item, listener);
+
+		if (item.isSelected()) {
+			checkBox.setChecked(true);
+		} else {
+			checkBox.setChecked(false);
+		}
+
+		if (item.isDisabled()) {
+			layout.setEnabled(false);
+			grayOutItem(true);
+		} else {
+			layout.setEnabled(true);
+			grayOutItem(false);
+		}
+	}
+
+	protected void grayOutItem(boolean gray) {
+		float alpha = gray ? GREY_OUT : 1f;
+		avatar.setAlpha(alpha);
+		name.setAlpha(alpha);
+		checkBox.setAlpha(alpha);
+		info.setAlpha(alpha);
+	}
+
+}