Let atoms bounce both vertical and horizontal walls of the rectangle

[#55054750]

...during single integration step.

TODO: should it also apply to other collisions?
Use Float64Array as base float array type

[#55054750]

It fixes problems with collisions.

Detailed explanation:
https://groups.google.com/d/msg/lab-models/qMfmI090Hvc/lPsDCIPLd4IJ

Benchmark results:
https://docs.google.com/spreadsheet/ccc?key=0AvPwgfkGGmTYdGFXYURseFdlUkZocXVOcVlqTEpRenc#gid=0