完成后台广告模块，首页广告图接入

Change-Id: Ifd698596afe7a87835fa297fa3dddb7a9136f763
Merge branch 'master' of https://github.com/Hahn-/GdutExchange.git

Conflicts:
	Public/assets/slide2.png
	Public/assets/slide3.png

Change-Id: I55e8e4f998e50457a32153b3c8d2b145f88113fb