Add functions to update on conference changes.

+ Add onConferenceChanged() to Connection, so that the Connection can
make act on changes to the conference.
+ Add a utility function to PhoneCapabilities to remove a capability
from a PhoneCapabilities bitmask. Figure this abstracts some bit
logic away to make things more readable.

Bug: 17429707
Change-Id: I0c97731a95dd6573488cd10f094a63abe2428bce

telecomm/java/android/telecom/Connection.java

@@ -911,6 +911,7 @@ public abstract class Connection {
             mConference = conference;
             if (mConnectionService != null && mConnectionService.containsConference(conference)) {
                 fireConferenceChanged();
+                onConferenceChanged();
             }
             return true;
         }
@@ -1009,6 +1010,11 @@ public abstract class Connection {
      */
     public void onPostDialContinue(boolean proceed) {}
 
+    /**
+     * Notifies this Connection that the conference which is set on it has changed.
+     */
+    public void onConferenceChanged() {}
+
     static String toLogSafePhoneNumber(String number) {
         // For unknown number, log empty string.
         if (number == null) {