Implemented retweet counter from twitter.

Signed-off-by: Mikhail Ramalho <mikhail.ramalho@gmail.com>

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# On branch tweego-0.3
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#	modified:   src/applicationItems/timelinesettings.cpp
#	modified:   src/backend.cpp
#	modified:   src/twitterapi/entry.cpp
#	modified:   src/twitterapi/entry.h
#	modified:   src/twitterapi/xmlparser.cpp
#	modified:   src/twitterapi/xmlparser.h
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#	Makefile
#	src/Makefile
#	src/build/
#	src/qrc_res.cpp
#	src/release/
#	tweego.pro.user
