ProblemsSolutions can now contain ProblemLines

scrolling is faster
ProblemLine -> VisualProblemLine
non rendering components stay in ProblemLine
Detects mouseclicks in problem boxes

Basic zooming
Added rendering inside of problems

Added descriptive headers to all classes
Changed the way the inside of problems render
Zoomed problem widths are consistent

fixed #7
Added zooming out 1 level at a time
Bug fixes

Updated TODO
fixed #6
fixed #9
closed #2
closed #1