Added -fPIC option to cmake files

Build system fixed, unused vars removed

External gtest dependency removed

Diameter optimized

Convolution simplified

Some optimizations

Convolution optimization

Fix for mass center when mass is absolute zero; Workaround for floating-point errors when grid beginned from one element in center of grid

Fix for convolution in case of multithreading, empty() method added

IScalesConfig interface segregated. DiscreteScales class now is default scale determiner

Convolution with exclusion implemented

Templated convolution added. Corresponding tests added

Unit tests for convolution with coloumb function works

Octree works over shared_ptrs now

Element with reference to mass added. Convolution tests does not work