WARNING! This patch depends on D61!

Notes:

• Makes '$' shortcut much more useful.
• Allows to remove the NUM_NULL_ONE hack used for size/scale like values!
• Complexifies a bit the code.
• In general, all those "transform" code could use some cleanup and tweaks. Only did the minimum required by this patch here.
• Code here is complex, would need careful testing!

Also, there are some issues with editmesh uses (+/- used as event, so eaten before reaching
handleNumInput(), no propper use of numinput-generated string for the header text, etc.).
Would rather fix this in another commit/patch, to avoid cluttering this one.