Added more Line functionality. Added function for drawing first of lines

- Line objects now have a slope and a slopeAngle (angle relative to
x-axis)
- Line object can calculate slop and slopeAngle from new points,
slopeAngle, or slope
- added 2 functions, averagesForSampleSections and calcVerticalLimbs
- averages used to find average sample values, given an array of
samples and a number of sections
- calc vertical limbs adds limbs to a given branch, and determines the
limbs line attribute based on picture size and array of averages
returned from averagesForSampleSections