New translation initialization

[RodenLuo]

First, expand the active region by a user-controlled amount of grids on each axes, and then perform uniformly spaced sampling on the grid indices in the hope of getting more or less uniformly spaced sampling in the Angstrom unit.

[RodenLuo]

After the discussion with Tom (details in #17), drop the expanding now. Later, if we have a decent amount of "hang at the edge" cases, we can run experiments to set a guideline for how to set the possibly to-be-added parameters