All versions of Smart Photographic Calculator

* 2D graph engine for expressions is improved. * Plot graph for 2-variable and 3-variable implicit functions. Note that implicit function must be an equation, not assignment, i.e. x**2+y**2=4-z**2 is invalid while x**2+y**2==4-z**2 is OK; * Change behavior of functions size, zeros and ones; * Performance improvement; * A number of bug fixes for Android N and above;