[SofaComponent] Fix computeBBox()

[fredroy]

Some computeBBox() functions were still using numeric_limits::min() instead of lowest().

numeric_limits::min() returns 0 (more precisely a value very close to it) if T is a floating-point type, whereas numeric_limits::lowest() returns -inf(more precisely -max of T), which is the expected behavior in computeBBox().

http://en.cppreference.com/w/cpp/types/numeric_limits/min
http://en.cppreference.com/w/cpp/types/numeric_limits/lowest

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