Updated to 1.7

- Added CheckBox object.
- Added RadioButton object.
- Added Slider object.
- Added converter.
- Added color theme "Fire".
- Added "load" attribute to some objects and removed the
"getVariableValue" and "getProgressBarValue" functions.
- Improved editor GUI.
- Implemented "mouse_drag" support for objects and the editor.
- Changed the event handling of buttons: The user-function with the
button's objID attribute (instead of the param attribute) as its name
gets called now.
- Added a list editor and removed the old way of setting the elements of
a List object.
- Renamed "elements" attribute of the List object to "Items" (Just
trying out whether it looks better that way).
- Renamed most tables to have an uppercase first letter.
- Bugfix: Graffiti crashes after writing something into an Input-object.
- Bugfix: The move- and scale-pixels of a ProgressBar object had an
incorrect position when it was facing up.
- Bugfix: The Input object isn't read correctly when it was inside a
container.
- Bugfix: The program crashed when you tried to load a non-existent
window.