[PythonCAD] Leader arrow sizes and dimension endpoint size updates

[Art Haas]

Hi.

I've commited some code to the repo that allow you to set the size of
the leader arrow or the size of the dimension endpoints. Instead of
these values being the default "1.0" units, they can be adjusted by
boxes in the two preference dialogs.

Edit - Preferences - Miscellaneous - Leader arrow size
Dimension - Preferencnes - General - Endpoint size

Yes, having two seperate preference dialogs is dumb. Eventually these
two dialogs will be combined into a common Preference dialog. I'm
leaning to doing a Preference dialog similar to that in Mozilla, where
the left side has a TreeView with all sorts of options, and the right
side shows the various options for whatever option you have selected in
the TreeView. I think this approach will provide a means of presenting
lots of different preference options in a managable manner, but I
haven't begun coding this improved Preference dialog yet.

I've also done a little work regarding the storing of global and image
specific options, so if you grab the code there are more things printed
out when it runs.

Another nice new thing in the repository code is that PythonCAD will now
prompt you to check and see if you want to overwrite an existing file.
Previously it just wrote to whatever filename you provided via "Save" or
"Save As" commands. Now a confirmation dialog box prompts up and asks if
you really want to overwrite the file. My quick testing showed this
works for me, so give the new code a looksee.

Art
-- 
Man once surrendering his reason, has no remaining guard against absurdities
the most monstrous, and like a ship without rudder, is the sport of every wind.

-Thomas Jefferson to James Smith, 1822