Initial infrastructure to show post contents

-Changed layout of Add Source Fragment to allow actions before after a
button is pressed and before the dialog is dismissed
-Still trying to make the Feed Content fragment to notice and act when a
post is clicked in the ListView... not successful yet...
-When screen is rotated, the state of the action icons (show/hide) is
retained
-Basic infrastructure to load post contents on Post Content fragment,
whether it replaces the Feed Content fragment or is shown in the right
side (tablets, landscape)
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