Making the UI more intuitive

[Serenacula]

Heya,

So, these changes were mostly for my own benefit, but I thought I'd offer them incase anyone else was interested. I've never used TCL before, so the changes may be a bit hacky, but they seem to work so far as I can tell.

I've changed the controls to be more intuitive:

• Left mouse button on the blank canvas now scrolls, rather than makes a selection box. Boxes still select and drag like normal.
• Ctrl+Left will do a normal selection box. (Previously Left)
• Shift+Left will allow you to select new things without unselecting the previous things. (Previously Ctrl+Left)
• Scroll wheel now zooms in and out. (Previously scroll up and down)

Everything else should behave the same as before, middle button and left+right buttons will still scroll like normal.

Bugs found:

• Left+Right snaps back, if you started out dragging something.
• When holding Ctrl or Shift, it uses the old selection behaviour if you click-select rather than drag-select

1.
The main bug I could find with this is that I cannot for the life of me work out a way to be able to scroll with left+right, while also dragging something. If you are dragging with Left, then hold Right to scroll, the camera will snap back to where you were when you started dragging. It is not a big problem, but it can be a bit annoying for moving an object across the canvas.

2.
I only just noticed this, but the new Ctrl and Shift functions don't work properly if you're click-selecting. This is presumably because this is handled elsewhere in the code, but the issue is too small for me to care about searching for it. The work-around is just to move the mouse a little when you want to select stuff.