Modernize default ctor definitions.

Made sqrLength() private.

Method does not make use of any part of Vector3.
If the functionality is needed it can be impl. outside of this class.

The TemplateVector3 is derived from TemplatePoint<T,N>. There isn't a
constructor taking 3 values for TemplatePoint. Instead of this a std::array
is used to initialize the TemplatePoint data structures. For this reason
the TemplateVector3 constructor that is taking two points to initialize
the internal data needs an initializer list.

- Implemented class template GeoPoint (see GeoLib/Point.h) and substituted class templates in the typedef.
- Some changes due to changed namespace in MathLib/Vector3.h and GeoLib/Color.h.