harmonic: Add grid cell count control.
harmonic: Handle smoothing edge case.

Don’t smooth if no interior cells exist.

Additionally, lower the maximum opacity of drawn weights to better
differentiate between boundary and interior cells.
harmonic: Rename cellCount to resolution.

resolution is more technically accurate and does not conflict with the
actual number of grid cells.

Additionally, in the bresenham function, rename count parameter to
width and check for out-of-bounds grid cells.