findHomagraphy can return empty Mat in master branch

Currently, there are different default typedefs for Point_, Size_, and Rect_. This pull request at least makes sure that default typedefs exist for int, float and double variants of each of these types.

Changed the signature of the minEnclosingTriangle function such that it returns the area automatically. Moreover, the overloaded function was no longer required so it was removed. Sample code, documentation and unit tests were updated correspondingly.

Removed the cvMinEnclosingTriangle function since the C API will be deprecated starting with OpenCV 3.0

Added erGrouping function: Find groups of Extremal Regions that are organized as text blocks. Updated sample/cpp to use the complete text detection pipeline

Added a namespace and prefixed global variables with "G_" in order to prevent variable shadowing problems.