Add a few features to the layer selection shortcuts system

[Daxel]

I think Moho could add just a few more options to make all layers selectable and that would be amazing to work with. If we had a "select closest parent bone layer" shortcut and all these three shortcuts could be repeated again to go further, we wouldn't need to touch the layer panel, to have a huge one or to use script tools to make buttons. For example:

Alt-right click: select clicked visible layer (as is) but if you press again alt-right click, Moho will repeat the process but ignoring the last selected layer, so it will select the layer underneath. Super useful when you have references on top of the layer you want to select, when you have masks etc, very often. Also if you click on a bone it will select that bone layer.

Shift-Alt-Right click: select group of clicked visible layer (as is) but if you press it again Moho selects the parent of that group. Useful very often, when you have complex characters, when you have a switch with groups inside because you need them to make different masks for their drawings etc so the direct parent group is not enough.

Ctrl-Alt-Right click (unused right now): it could select the closest parent bone layer. If you do it again, it will ignore latest bone layer and will select the next parent bone layer. Probably the most needed feature because Moho animators and riggers need to go to the bone layer super frecuently and if we have many layers it forces you to have a huge layer panel and even then you have to scroll sometimes if you were working on a bottom layer or a nested layer.