Add start position option.

[63BeetleSmurf]

This pull request adds a new option allowing you to specify the start position when creating a new note. I tend to close notes when finished with them so often use the tray icon (or hot key I have setup, see #127) to create a new note. This results in it being at the top left which usually means I need to move it to somewhere less intrusive. Notes created using the + on another note will still open relative to their parent.

Scenarios;

1. When developing I tend to have my IDE on the left half of the screen with the right split between documentation and terminal if needed. This means the least intrusive place for notes can be the bottom right if I'm not using a terminal, or the centre right if I am.
2. When I am working with GIMP, I find the bottom left to be the lease intrusive.

This new option give a huge usability improvement when used in conjunction with a keyboard shortcut for a new note which is possible with my command line modification: #127

[clefebvre]

Merged on master.