View mode movement

We have discussed it with @occivink but never implemented.

The idea is to allow scrolling past the main cursor by using highlighters to visualize the selections and restoring them (selections and view) when leaving the view mode.

Removing the single v, moving V (lock) to v, and adding a bunch of commands, such as g / G, Page Down / Page Up and mouse bindings.

@mawww What do you think to allow scrolling past the main cursor in the view mode?