conversation view: add call buttons

- add audio/video call buttons to message page header
- clean up button UI
- set messageList maxWidth and center in view
- fix incoming message selection bug

Change-Id: I74fe2a8760eb23198d14007cbfb045222813a667
diff --git a/invitebuttonswidget.ui b/invitebuttonswidget.ui
index e1f8bf2..e3caf2e 100644
--- a/invitebuttonswidget.ui
+++ b/invitebuttonswidget.ui
@@ -108,7 +108,7 @@
      </property>

      <property name="icon">

       <iconset resource="ressources.qrc">

-       <normaloff>:/images/icons/ic_clear-24px.svg</normaloff>:/images/icons/ic_clear-24px.svg</iconset>

+       <normaloff>:/images/icons/ic_clear_24px.svg</normaloff>:/images/icons/ic_clear_24px.svg</iconset>

      </property>

      <property name="iconSize">

       <size>

@@ -140,7 +140,7 @@
      </property>

      <property name="icon">

       <iconset resource="ressources.qrc">

-       <normaloff>:/images/icons/ic_block-24px.svg</normaloff>:/images/icons/ic_block-24px.svg</iconset>

+       <normaloff>:/images/icons/ic_block_24px.svg</normaloff>:/images/icons/ic_block_24px.svg</iconset>

      </property>

      <property name="iconSize">

       <size>