[logo] Add AliceVision logo 170x170 (alicevision#354)

Author: gregoire-dl

README.md

@@ -1,4 +1,5 @@
-![AliceVision](https://github.com/alicevision/AliceVision/raw/develop/docs/logo/AliceVision.png) AliceVision - Photogrammetric Computer Vision Framework
+![AliceVision](https://github.com/alicevision/AliceVision/raw/develop/docs/logo/AliceVision_170.png) 
+AliceVision - Photogrammetric Computer Vision Framework
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 [AliceVision](http://alicevision.github.io) is a Photogrammetric Computer Vision Framework which provides a 3D Reconstruction and Camera Tracking algorithms.