PAINT-18_respect_aspect_ratio tests added
code for respect_aspect_ratio added to BaseToolWithRectangleShape.java, tests work localy on physical device
isCorner check optimized, test works on two different physical devices, achieved by alternate bigger and smaller resizing
Merge pull request #190 from Catrobat/PAINT-18_respect_aspect_ratio

Paint 18 respect aspect ratio
accepted: @X4mp [ru]
implementation: @cbenkovic [cb], @AlexWieland [aw]