added flow control to prevent the user from drawing, validated numbers.
Users cannot access the other functions until they create a canvas
first, nor can they use the spinner to enter elements outside of the range. They can, however, still enter invalid points (but we sill have
 error handling in place to catch that.i)
Merge pull request #4 from TheSpiderPig/fix_validation

added flow control to prevent the user from drawing before the canvas is created and added limiting to the number in the input boxes to match dimensions.