Grid enchancements

@vidhyalongani is already working on this.

Since Aug 5, 2022.

For the grid, the client asked for the following enhancements:
1) the relative size of the grid and its content in the 2D viewer gets larger and occupies large portion of the 2D viewer (now there is a lot of empty space around the grid);
2) The grid becomes bigger and ranges 2.5mm (or 2.6 in width) x 2mm (height), the slice will be at the center and have some empty space around it. The range on the y axis would be 2.5 mm, with the first/last numbers displayed -1.25 and 1.25, for the y axes the range is about 2 mm. The pitch of the ticks should be the same on both axes (0.1 mm ideally), we can display numbers every 0.4 or 0.5 mm as it works best as long as they're mirrored around the 0 (see below);
3) The numbers on the grid are mirrored, namely same values on the left and on the right of the 0 (same goes for above/below the 0). For example if the numbers on the right are 0.4, 0.8, 1.2, 2.4, the ones on the left will be the same (except negative);
4) It is hard to understand to which tick the number refers to, could we make the tick associated with the number a little longer or thicker or more obvious that it is the one associated with the number?
5) the 0 on the x axes seems a little off (I could be wrong);
6) The 0 of the z-Axis is in C8 caudal, not C8 rostral (they changed their mind);
7) Add the unit 'mm' on both axes, where it fits best;
8) The z-axis indicator which is now a number in the top right corner should have the label: Z-axis position (center in C8 Caudal): XX mm; (and maybe move it inside)
9) Possibility to toggle the grid on/off;
10) Bonus feature (add on to feature 9, it is not strictly required but a nice to have): the grid exists in three states 'off' (it's not there), 'frame' (it's there as we see it now, so a frame around the slide), or 'grid' (where the major lines of the grid -- so not all the lines at 1 mm pitch, but the ones associated with the numbers, so the ones at 0.4 or 0.5 mm pitch-- are overlaid on top of the slide). The toggle switch should be somewhere in the 2D viewer. this one might be hard to maybe tackle it last.

I know it does not sound like it, but they did really like the first version :-)

@zsinnema @afonsobspinto some of these tasks are probably more FE so I asked @vidhya-metacell to help us (she has hours for Salk in August). I am not sure what would be the best way to split up the work so I let you guys take a look at it, ideally this would go for sept 1 but there are some other important BE tasks for that date.